big worlds, big problems

What would it take to make a large world work? I'm talking of MMOGs with worlds bigger than Manhattan. One of problems with huge worlds is that unless you fill it with lots of content, there will be vast expanses of empty wilderness, and there would be long tedious travel times involved.

That's assuming that the whole expanse is part of the game from the beginning.

Imagine a world which has vast wilderness areas, with pockets of civilisation along one edge - perhaps primitive colonies on the coast of a new world. Everything you need is pretty much within close distance, but the frontier beckons. You could, for instance, set off into the new world and never see a civilized soul for days at a time.

Add to this the possibility of player impact on the world, something deeper and richer than simplistic "player housing", and this vast empty wilderness might slowly fill up.