So according to Cold Iron Studios there are 20 enemy types in total, right?
I'm sure other have listed all the verified types already somewhere in this thread, but I haven't been very active on these forums for months now (maybe years even).
Described or seen in vids, pics and announcements so far:
1 - Runners
2 - Warriors
3 - Drones
4 - Praetorians
5 - Prowlers
6 - Bursters
7 - Spitters
8 - WY Combat Synths A (Rifles & white body-armor)
9 - WY Combat Synths B (Pistols & black body-armor, red eyes)
10 - WY Combat Synths C (Heavy weapons & white body-armor including helmets)
11 - Melee Working Joes
12 - Exploding Android Remains
13 - Pathogen Stalkers
14 - Pathogen Poppers
15 - Pathogen Husks
16 - Facehuggers / Eggs (not verified but will be in the game...?)
17 - Queen (somewhat, kinda, sorta verified but will be in the game for sure...?)
18 -
19 -
20 -
...So that leaves us with two (in case one counts Facehuggers and Eggs as two separate enemy entries/entities or not), arguably three open enemy slots.
I think it would be cool if there was at least one more Pathogen enemy type (maybe something akin to the Newborn, but more Pathogen-looking), some kind of hulking WY robot, like a tank-tracked Defense Robot or an combat synth controlled Exosuit ...or maybe even a manic Working Joe inside a Powerloader (...just kidding!). If there is a third slot left I think it would be rad to see a larger sized Runner (call it a Dragon even), similar to the Alien Mothers in the Alien 3 SNES game, or maybe just reintroduce the Crusher since the Prowler pretty much looks like the Crusher already. Should obviously be very rare and more of a boss than anything.
Then we have Chestbursters, but I doubt that they qualify as a designated enemy type. Hammerpedes would be neat though, but I feel like they are limited to flooded or boggy areas, or tall grass areas, and I can see them getting annoying and old really fast. You could say the same thing about Facehuggers, but at least you can stop them from emerging by destroying those Eggs before they have the time to get out to attack you. Also, Facehuggers can climb walls and ceilings, i.e. you won't have to run around focusing at the ground, which always gets annoying after awhile.