I think it'd definitely be cool to see some wildlife that could be odd, interesting, dangerous, or all of the above. I definitely liked the introduction of the "Mother Crab" First time I encountered it I freaked out, because it landed far enough away not to crush me, but close enough to knock the gun down out of my hands and crush it.
I say this in part from my own interests, but I think it'd be interesting to see an animal/actor that could pass through terrain without interacting/destroying with it, but could collide and engage in combat with other actors. E.g. Graboids, tremors, sand-worms, giant worms, any kind of worm-like creature that would erupt forth from the soil with a gaping maw, and then retreat back to the safety of the ground. Not only would that be awesome and intimidating, but it'd be equally awesome to take control of one yourself and go around eating clones.
In general, more wildlife actors who are effective with melee/unarmed combat...spitting creatures could be cool too, though. Especially if you get some acid in the mix and do that cool little skeleton-swap Grif is sporting.
I think it'd also be equally as fun to play as a colony of native wildlife defending its hive/lair/nest against armed clones and dummies, as it is to play as a brain in a bunker against those same odds.
One game I thought always had an interesting assortment of fauna was Command & Conquer: Tiberian Sun. In particular, a creature in the game called viceroids. They were the result of what happened when organic materials decomposed in the presence of tiberium. The matter broke down into simple organisms that would join together into a colony to form a bigger creature, and would travel around as a writhing blob in search of more organic matter to consume. Normally, they are small and harmless. But when two or more viceroids joined together...they made an "Adult" viceroid, which in all respects was essentially "The Blob" straight from the horror flick. You would have to send an entire detachment of your forces if you hoped to combat it. It did massive damage to vehicles, and when it devoured infantry (which it could do instantly) it would regain health. I'd imagine if faced with something like that, you'd find great use in playing as the dummy faction.
Though I'm sure between Data and Prom they've got a massive compendium of resources for creature ideas.
I think a variety of wildlife could also make for some interesting missions. Say, Tradestar is interested in some of the natural abilities and chemicals the creatures on the planet utilize. Your mission: to capture various benign and deadly animals, alive and return them to Tradestar.
"We want 5 Mother Crabs, 3 Worms, and 1 Adult Viceroid"
"FFFFFUUUU"
"Wait...better make it two Viceroids"
Bit long, I know...
But the idea of killing clones by eating and melting and mauling them makes me giddy.
