Infected Spawn and Evolving Upgrades
I have no idea how realistic these requests are, however:
Would it be possible for aliens to spawn a la xenomorphs in the Alien movies?
Say, a dragoon's ranged attack marks a human as "infected" (or perhaps an "Advanced" Dretch that carries with it an infected bite.) Then, infected humans below a certain health threshold have a chance to spawn an alien that's in the queue.
Infection might carry with it a poison effect that works to drop them to the required health for spawning an alien. Perhaps there would be no effect so a human does not know they carry infection. Infected humans might also appear to have a green overlay to the eyes of other aliens, so they know which ones are marked for doom. Obviously, health pads and medkits could counter the infection.
Evolution upgrades might make for an interesting way to broaden the scope of alien tactics available by allowing certain aliens to "evolve" traits such as carapace armor, enhanced tendons for jumping, sharpened claws for increased armor penetration.