Ok so you've seen the likes of Terragen 2 with its stunning 3d fractal planets ... the ability to fly all the way out and through the atmosphere and beyond into space, and then right back down to the level of pebbles on a beach, all fractally generated. Entire planets done this way. And especially, land features that include overhanging parts, caves and bridges. This would be totally awesome.
Also it would be great to have some procedural texture generation and some other tools to create procedural content - this can be a huge time saver.