I'm not too worried about 0ad's current limitations because of one thing: it's open-source.
My issues with diplomacy are already being discussed by official and unofficial devs. (Ideas about a "loyalty" meter have been talked about positively.)
I wouldn't be surprised if a "War of the Ring"-esque mode was introduced in the future. Hopefully it would function a bit more similarly to Total War.
I think Neph was saying he'd finish the faction overhauls before dropping support. So no worries!