Regarding the Mime Jr. situation, I've seen speculation that Smeargle has been held back so long because they intend to use it to replace Mr. Mime as the European regional. Decent theory in my opinion, but we'll see.
As far as the new regionals go, they did make a lot of gen 3 regional, but in gen 2 there were only 2 regionals. So maybe they just make 4 new ones and call it day. Or they could make Rotom's different forms regionals which I think would be a pretty fun mechanic.