4D Minecraft?

So there is a 4d platform game that I have been waiting for forever:

http://miegakure.com/



Its taken so long that I've considered making my own.  In fact, I've already wanted to try my hand had a voxel based game like minecraft.  What if I made 4d minecraft?

I would think that no matter what, for convenience you want the y dimension fixed because of gravity (it would suck if x,z,w was being renderer and everything is mysteriously changing as you fall).  Then, either you switch between x,z and z,w and x,w OR you show x,z and use w as some kind of weird dimensional shift.  Either way it would be pretty sweet.

Also, obviously, it would use JRuby for a mod interface so the stupid fucking mods can be loaded at run time, from like a gallery or whatever.