Im pleased FS is doing 40k version of Vermintide 2…and i have no doubt game will be a masterpiece.
However, I dream of v2 style, survival game where group of survivors (civilian or military) must survive into planet isolated by Tyranid Hive Fleet… chaos is nice yes, but what brings more survival instinct into players than Tyranids ? 
I don’t think they will put Tyranid, as they are not really allied with chaos.
Chaos might ally with the Imperium to face the Tyranid threat (as they are not useful to the Great Game)
If the game is successful I can imagine we’ll see new enemy types like they tried with VT2. As to whether it’ll stick with chaos or introduce other factions for new enemies, that’s up in the air. I’d hazard a guess that we’ll see new chaos enemies though rather than other factions as its easier to add piecemeal a few enemies at a time rather than whole factions. But I’d love to be pleasantly surprised.
Sounds like you dont want a Vermintide like game then, V2 is a hack n slash.
It has no survival aspects.
I’d suggest the old AVP game.
Also remember normal humans in 40k are not “Heroic” like normal humans in Warhammer Fantasy are, a base Hormagaunt can kill 3 Guardsmen by itself so long as its in Synapse range. Imperial Guard only ever hold vs Tyranids thanks to huge numbers and tanks.
Add in Traitor Humans and more varied chaos.
Leave Tyranids to a space marine focused game like Deathwing.
Chaos… Allying with the Emperium???
What are you on and can I have some?
That would never in your wildest dream happen, even if the Tyranids posed a huge threat to both sides (they do). No.
The entire reason for the war between Chaos and Emperium are high ranked traitors in the Emperium gone Chaos and on multiple occasions have tried to invade the Emperium. The Emperor would never let the fact that some of them generals betrayed the Emperium slide.
Well it already happened a few time
In 30k, yeah, they teamed up - on occasion to suit their own needs and rarely more than Marine Squad needed help with Event A and Chaos Squad did too. There were never any formal alliance between the two - and should their higher ups (mostly Imperium) have caught wind of it, you can be sure the offenders would have been punished accordingly. After which they always went back to murdering each other given half the chance to do so.
In 40k there is simply nothing that threatens either side enough to even remotely consider an alliance and their hatred towards each other runs so very deep. There’s nothing to obstruct the Warp and there’s nothing to obstruct the Emperium. Yes, there’s the occasional Tyranids, but they don’t really bother the Warp in which Chaos reside, they are a nuisance to the physical realm and rarely bring more than a single fleet to the table, nothing that the Emperium can’t handle should they care enough.
In short, nope, not happening.
Secondly, it’d be weird to introduce Tyranids as an enemy. They consume Worlds, there’s nothing left after they’re done. Whats our business there? To stop them consuming a world? The campaign length would have to be much longer than all of Vermintide 2 base game + DLC + FLC in order to reflect such an enemy proper.
Tau, much more likely to be introduced. Damn Xeno’s sterilize and/or euthanize anything and anyone that don’t comply which could be done in a 4 map or so campaign (god not another WoM single map fiasco).
Would be sweet, but Orks would be even sweeter!
Are they not working on Orks in V2, oh boy they can Port them over. Imagine all the really funny Ork Speeches XD.
That would be a nice 3 Front fight!
I remember reading that fatshark said that they are going to stick to Nurgle themed scenarios, and I dont think that Darktide is going to be an exception given what we have already seen from the game. Although, we can never discard the possibility of new factions in DLCs, but honestly I dont think we are going to see Tyranids. If you wanna fight them you can try Space Hulk: Deathwing (if you havent already).
Honestly i’m a little sad to hear it’s chaos again due to the fact it feels like copy and paste and there has been more than enough games with chaos in it. As for the Tyranids i would just go play death wing so that why they decided to avoid using them.