Okay so Minecraft is coming to XBLA now, what about Windows Phone? Imagine creating a world on your Xbox, and then being able to access that world from anywhere on the go! A Minecraft world in the cloud, this must happen.
Microsoft do appear to be moving down this road; multi-platform gaming, that is, but I don't think it'd work for Minecraft, simply because the worlds can get too big. Generally the sort of cross-platform data that goes across live is simple "What is the other platform doing?" sort of traffic.
Maybe a regular client might make it's way to WP7, but I imagine developer interest would be low at the moment, so I wouldn't get your hopes up unfortunately.
If you want a "world in the cloud" just spin yourself up a private server; with only one person accessing it, it won't impact your system performance much if at all, then you can connect from wherever you like, provided you can get the MC client, of course.