I would include "native" or "mini-factions" as post-release free DLC (probably as part of our post-release patches, to sweeten the deal). And then I would only use them in scenarios and skirmish maps, so that they can be used judiciously and uniquely by the designer. I'd rather they be a "special" feature of some maps rather than something that's used all of the time in random maps and whatnot. They could also be useful in campaigns. To make sure they are actually implemented, it is best to think of ways to include them without much extra programming. Try to think of things that we are going to include anyway, then just build on those. For instance, best to think of a way to use the planned 'capture' feature and integrate that into your plans instead of coming up with a whole-new way of doing things. This way, your pet feature (in this instance, mini-factions) is easier to implement, making it more likely to be implemented. Just my advice.