There's already a similar thread over in the Mod developer's forum, but there isn't a whole lot of talk about actual gameplay, and it'd be more appropriate here. I've been digging through the game's files and found a couple of unimplemented structures & units. Bear in mind, these are unimplemented, and some might very well might not end up in the final game. Commanders Beast: Short, stocky biped with no arms and shoulder armaments of some kind. Imperial: Generic bipedal bot, probably a base for other bipedal models. Raptor: As the name implies, its a biped but with a more lizardish profile. Spider: This is probably that 4-legged commander they were talking about. Looks pretty insectoid. Land & Air Fusion Plant: Now I guess we should expect a couple of additional resource structures (I believe wind & solar were suggested at one point), If I had to guess this is more powerful & expensive than the advanced plant but has certain restrictions. Uranium points perhaps? If its destroyed, it blows up your base? Who knows. Megabot: Distinct from the Slammer (aka assault_bot_adv). Definitely not a commander. No idea what it does, though. It still looks pretty rough, but I can make out what looks like two quad-barreled gun turrets, and what I think might be a pair of shoulder-mounted missile racks. One arm looks different than the other but I can't really tell what they might be. Tank_Heavy_Mortar: This might be the Thumper we saw from the earlier builds. How a mortar unit would be distinct from an artillery unit is something I'd like to see worked on. Unit Cannon: The man cannon we saw from the trailer. Doesn't look all that different, probably will be added when we get orbital. Gunship: This doesn't look much different than the unfinished gray model we saw on the uberstream. Odds are they're still debating if a gunship can be balanced. I'd at least like to see a more finished version. Bot Artillery & Advanced Bot artillery: Now this is interesting, it implies there should be a basic-level version of the Stomper. Perhaps the stomper had been intended as a basic-level artillery, and that two-barrel version from the earlier builds is the advanced version? Orbital Factory & Advanced factory: This looks like its supposed to be a floating landing pad of some sort with a comms tower, so I'm not sure if it can be built on land. Satellite & Advanced Satellite: Pretty self-explanatory. Not sure if it'll be geosynchronous or free-floating, but I hope it also has a wider sight radius than radar does. Orbital Lander: Likely the same unit we saw in the trailer. Orbital gas mine: Resource collector for gas giants I assume, though I'm not sure how its supposed to draw metal or energy from gas. Launcher & Advanced Launcher: Still not sure what the difference will be between tier 1 and tier 2, but it's most likely those rocketpads.
Did more digging, found the unit images for some of the things mentioned above. They're small but you can make them out. I had the bot artillery and vehicle artillery thing backwards, apparently.