OK, OK, I'll admit. I haven't read all of the responses, but the thing I would like to see is a new and better engine. No offence, but the new engine has too stiff animations, I simply don't like it. The best engine, in my opinion, is the one from Avernum 3, so I think it'll be either that or a brand new one. And AFTER Avernum 6, I belive Avernum Online is the way to go. I would join the SECOND it would be out. I don't think It's just me, I bet other people would be thrilled to get in.
I don't think a new playable race would hurt us. HINT: Vahnahtai