So I've been thinking about Predaliens and what role they could possibly serve in the hive. Generally, they seem to be sort of a heavy assault unit, with all examples so far excepting Chet seeming to fit this description. They serve as bosses (or at least minibosses) and are the main antagonists in whatever story they happen to be in. Indeed, the Predalien is nothing to be taken lightly.
The Earth Predalien seems to be anomalous. For reasons completely unexplained, instead of being a super-warrior, it was somehow a juvenile Queen Alien in addition to being a superior combatant. Even in the movie, there was no indication given that the Predalien was trying to become a physical, full-fledged Queen. Sure it built a hive, but Xenomorphs have been known to do this anyway in the absence of a Queen. It seemed to me the Predalien was simply acting as a Queen, in that it was the only one who could produce chestbursters via direct impregnation of the host (something else that is completely unexplained). My theory is as follows.
In the Absence of a Queen and a Xenomorph that would normally take her place, the strongest or smartest of a lower caste will begin to evolve. It's possible, even, that a Queen may somehow choose her "successor" among the lower ranks of Xenomorph, maybe even over a higher ranked one. Seemingly, the Matriarch had a unique connection with Specimen 6, sensing it's unusually high intelligence and designating it as the one xenomorph who would free every other Xenomorphs. Other warriors simply run about causing havoc, while Six has directions and objectives and purpose. Six isn't the only "Lead Alien" to be seen. The Lead Alien in Resurrection seems to serve a similar function. Grid seems to be the designated "Leader" of the Pyramid Hive, having killed two Predators and all. Queens can influence the evolution of certain castes of Xenomorph, as seen in Extinction. They can give specific directions to single Xenomorphs, such as 6, and their spawn don't sway from these directions. It isn't that much of a leap to say that maybe a Queen can influence the evolution of an individual rather than their whole caste.
It isn't impossible that the Matriarch herself was the cause of 6's abnormally high intelligence or that other Queens invest more in the intellect of one or several of their many offspring when in captivity, which is something these situations have in common. The Antarctic, Cloned, and Matriarch Queen were all in bondage. Queens who are not in bondage have never produced such unusually smart spawn because they don't need to. Back to the Gunnison Predalien though, it is quite possible that it was chosen as a chestburster (and that six was as well), obviously because the rest of the Antarctic Queen's brood and it's previous Lead Alien was killed. She had no choice and it certainly wasn't a bad idea to make a heavy assault alien your heir/lead/whatever.
Indeed, the Predalien seems to be intelligent even as a Chestburster. Other bursters just come out, regardless of who's around. This one waits til the exact moment the Predators walk out of the room. Could've been chance, but it seems more like intelligence. Like Dr. Groves said: 'Caution? A strong indicator of intelligence...' and Chet shows plenty of caution throughout the film, especially around the Predators. We never see Chet's growth cycle: she's seen as a chestburster then when we get our first real sorta look at her, she's an adult "Predatorian". However, around the very beginning of the film, there are a few seconds of her sloughing off molted skin, far more than would come off of a chestburster as seen in Alien. Lead Aliens have always been Warrior Caste. It is possible that Chet might've been a warrior before finally becoming a Predatorian and that this skin we see is all that remains of her Warrior phase.
If you look at the concept art, most of the Predaliens do not have crests and the whole "Young Queen" thing seems to have been added later in production. Indeed, their heads are the typical elongated, phallic shape that warriors and drones have. It was even said that the Queen-like head was "added". The Predalien seems to have originally been conceptualized as a warrior, but later turned into a Queen, and the only thing we might've seen of that, again, are those few seconds.
The odd reproduction method of the Predalien is unique to that individual-- we never see any other Predaliens do anything remotely similar and, again, they simply function as bigger and more powerful warriors. However, these other Predaliens don't seem to be "Predatorians" and their Queens are not only alive, but free. My out-universe explanation was that the creators of the movie added this function of the creature purely for the shock factor and didn't give it any real thought. There was no attempt made for any type of cohesion with the rest of the universe and I believe there was even some nonsense idea about "DNA acid" that the Predalien would inject via it's tail that would...turn the victims into Xenomorphs or something. Stupid.
However, if pressed for an in-universe explanation, I would say all Predaliens have the potential to do this once they morph into Predatorians. However, they only morph into Predatorians in the absence of a Queen. Otherwise, they serve a warrior function. Chet was something of a rarity in this case: the first Predatorian seen on-screen. The ability itself is probably unique to the caste and likely a variation of the prolific breeding rate of the Predator itself, thanks to the DNA Reflex. How many offspring a Predator has in one go is unclear, however the Hish, a close relative or variation of the species have 6 at a time. Dachande was known to have about 90 children. Belly bursters occur in sets of 4 or maybe 5, a similar number. Runners come from dogs, who can have up to 15 puppies in my experience, however the difference lies in the Xenomorph simply not taking as many traits from the dog. Predators have potent genes, which is why Xenomorphs take so much more of their physical and mental attributes, up to 15%.
Chet functions as both a Lead Alien and a Praetorian, a possibility once again demonstrated by 6. She is the Xenomorph most interested in propagating the hive and seems to have the most direction, but does partake in the occasional senseless murder. She's not a Queen, other aliens don't even really listen to her and she doesn't really seem to be controlling them. While in the sewer, she has to physically slap one warrior away, when she could've simply willed him away, to make a host out of the homeless lady. When fighting Wolf, other Xenomorphs do not assist her, even though protecting their future Queen should've been imperative as seen with the Runner and the Queen Burster inside of Ripley (also the Royal Facehugger could facehug twice, with the purpose of making a drone and then a Queen, with the drone protecting the vulnerable queen, so Xenomorphs DO care about an eventual queen as much as current one). The directors may say it's a Queen, but in-verse evidence says otherwise and, again, the movie itself makes no indication she's preparing to morph into a full-fledged Queen Alien.
My personal take is that Chet would've been "stuck" in a Praetorian stage or would've never completely reached Queen Status. If it is true that it went from warrior to praetorian without losing any of it's host's physical earmarks, it might've even been impossible for it to have been a Queen, as Queens are purebred Xenomorphs. Predaliens, Runners, and Warriors are transbreed aliens, but the difference between a Predalien and a Warrior is that Warrior and Runner aren't so overtly the product of their hosts. Praetorians look the same regardless of host and can be held up as the standard for a "pure" alien. Warriors and Runners don't differ from this look, but Predaliens largely do. Molting may not only change the size and caste of a Xenomorph, but it's genetic makeup as well, siphoning out the "foreign" DNA as a Xenomorph moves closer to a Queen (and, according to extinction, Queens and Praetorians are very biologically similar, if not identical). In Drones and Warriors and Runners, there might not be that much to change, which is why molting from caste to caste is so easy (Runners could be the precursor to Crushers. Warriors have been show to be one possible route to Praetorians) for them. However, something that is damn near 20% of it's host might just be too much to change. Xenomorphs are apparently very sensitive to the mixing of their DNA, as seen in the Spliced Xenomorphs who were unable to create a proper Queen. They got Rogue (Xenomorph), who was a sterile human/Xenomorph hybrid. Furthermore, the Queen with Predator DNA was said to be impossible and was only made possible by bio-engineering, in which is produced the Predalien Queen, an unnatural but functional hybrid. A true hybrid, female at that, and across the board female hybrids are known to be fertile in reality. Male ones of the same or similar crosses, such as Rogue, are not. If 10-15% (some sources say as much as 20%) DNA looks like a Predalien, which is vastly different in appearance than the purebred Praetorian and takes obviously from its host, then Drones, Warriors, and Runners must take far less DNA from their hosts, which is why they only have passing or very subtle similarities. At best, the Predatorian might have gotten larger and more physically similar to a Queen, but it would've all been superficial. It's method of breeding, which is arguably better than using facehuggers and eggs in some ways, would've remained the same. The Predatorian would've gotten as close as it genetically could to a Queen: Warrior (20%), Praetorian (15%), and the not-quite-queen stage which I'll call the "Regent" stage (10%).
Regents cannot lay eggs, like a Queen, however they can produce Royal Jelly, with which they would force down a hosts throat along with a single or several embryonic bellybursters. It is often said that Specimen 6 turned into a Queen due to coming in contact with Royal Jelly, but since she never encountered it as a chestburster, I don't think it makes a difference. Whether you break canisters or not she still ends up as a Queen at the end of the game, so this is obviously not a factor. I think, like bees, ants, and pretty much any other eusocial insect, royal jelly must be introduced early to an embryo for change to really take place. In the case of a single burster, there would be a single larval Queen who would grow up and rule of the Regent would come to an end. If there are several Queens, they would duel to the death as seen in Theories of Propagation, and the winner would take her "throne" from the Regent. The Regent's job is done-- it's Praetorian side 'de-triggers' as detailed in Exinction and it acts like a typical Praetorian or Warrior and the hive goes on.
In conclusion, Predaliens are basically beefed up warriors. Chet was a special case: a warrior -- similar to 6 -- who turned into a Praetorian due a lack of a Queen and/or by the will of the previous Queen due to being the designated "Lead Alien". Chet would've eventually settled down and turned into an egg-laying Queen, according to the directors of the movie OR she would've brought forth a true queen since transbreed aliens of that degree cannot truly rule, based on what we've seen and know of the aliens so far.