I'd love to see a much more improved version of XP. Some things that'd be nice is the ability to ADD layers to a map, not just 2 or 3 by default and then an event layer. IMAGINE THE AMAZING MAPPING POTENTIAL OF A LAYER-UNLIMITED MAPPING SYSTEM!
What I'd like to see though is an RPG Maker that not only helps out with the design of the game, but allows you to select a coding language (so if you're good at using XNA/C#, C++, etc., you don't have to adapt to something like Ruby).
And going back to the original topic of 3D RPG Makers...it's pretty summed up that amateurs shouldn't dive into the deep water of 3D RPGs. I'm sticking to 2D til I can iron out some aspects and learn to actually code my own system. I may have concepts lined up for 3D games (the ENTIRE Chaotic Fury series), but I will NOT act on them til I have enough knowledge AND enough experience in doing this line of work.
What I'd honestly suggest to those looking to work with making 3D games: Go work with an editor for an existing game within your genre and make a few decent mods. If you wanna make FPS games, go make a Steam Account, get Half Life 2 or Half Life 2 Deathmatch and mess around with the Source SDK (WHICH IS FREE).
Wanna make an action RPG? OGRE would be perfect, or just learn to mod Oblivion itself.
The list goes on...