I don't think that's a good idea.
I'd rather rework the units like proposed in wingflier's "let's remove hull types", because the discussion there just leads to a change in what units do and are.
About what units are "useful" and "not"... I think this approach and list is a waste of time because everyone can and will have his preference. Your focus should be in enabling modding to cover about 98% of what units can do, and creating maybe 30 "small" units, 10 "flagships" at most. If someone else wants "specific", he'll mod it and maybe, in the end of the dev run, you can ask forumers to build the remaining ones for you. Given what you made of the forum, it's a no-brainer that you'll find volunteers.
Basically, the only thing you need is the list of abilities to be modded in the game:
- direct damage,
- AOE damage,
- shield
- hitting
- decreasing health by time
- decreasing health by shot
- regeneration
- AOE damage divided by number of hit units
- eating other units
- immunity to shield
- damage resistance
- repair capability
- life stealing
- auto replication
- drone generation (by time)
- armor suppresion (acid whatever)
- teleportation
- carrier capability
- explosion on death
I think I forgot a few, but still. It's all that's really needed. You want to make modding a reality ? Then you should make use of it. Don't make yourself work MORE than you have to. It does not matter if someone likes ships or not. It's going to be moddable.
About game mechanics, well. I think basically it's covered in the "what makes AI WAR, AI WAR thread already".