It's not a bad idea. I distinguish between theme and gameplay. The theme is how the game is presented, e.g. story, characters, graphics. The gameplay is the rules of the game and what you do in the game to win or enjoy it. So when you talk about monsters and chalk outlines, that is the theme. Your theme sounds interesting and fairly unique. For gameplay, you would have to tell me more or show me a prototype before I could say if it sounded fun or not. For example, playing hopscotch could be realized with gameplay much like Guitar Hero or a runner genre game--and these are kinds of gameplay I'm a little bored with.

I think a more general block-pushing game engine should be created and people can add their own theme