Personally I think it is a monetary thing. 4J has commented on adding servers. With servers, I believe, we will see infinite worlds... it's just going to cost. This is also how I believe 4J will add in larger multiplayer support that they have been promising.
If I was a betting man, now that minecraft will be very close, if not on par with pc... Relms will be the next update.
Public forum man... get over it. Send a private message.