Speaking of power paths, will there be lava and cave-ins and such? Having a plate give out around your base and be replaced with some deadly red water would be kind of neat. I always liked levels that had lava flooding. You had to pay attention and maintain your power paths.
Random underground lava lakes would also be nice. It's always cool to drill through a wall and find yourself on a lakeside with a huge seam of crystals on the opposite side. You can see it but you have to think of a new way to get to it.