I think Google's going even more open source so the gap between Maemo5 and Android is getting a little closer.

Whereas Nokia is shifting away from Android and away from Maemo5 with Harmattan which is very iOS-like.

Still I think the closest thing to Maemo5 (besides MeeGo/Harmattan) is QNX only if RIM open sourced it. Its a very powerful OS from my experience, in fact sometimes I wish Nokia released the PlayBook (then at least they would've had a chance).