While others ask for the removal of tree stumps (which I think should become a real feature, as well as the removal of certain shrubbery), I really think it is a waste of rocks and soil to just blow up mountains. Why not use that material to fill rivers and lakes or expand the coast line? Or Use spades and dig holes or remove some cost line to put it somewhere else on the map?
Islands would not only look very individual, everyone would be able to create new building space in all kinds of areas. It would be such a great feature. Plus, BB could sell extra soil for ppl who really want to turn all the water into solid building areas. You don't need any building areas? By spades, remove your entire island (except for a small spot for major house) and sell all the soil to other players who can't wait to double the size of their islands.
Excavators ftw!