I've already started working on a second version for this game, because I enjoyed making it a lot and I think has potential! My immediate addition would be a level editor, because that'll also make MY job easier if I want to expand the game. Plus sounds, level stats, and other bells and whistles. But what you mention sounds also like a good idea - a sandbox/infinite mode. It should be possible. I'll put in the "things to be added after the fundamentals are down" list.