That wasn't an angry face, it was a disgruntled face. And think about it: There are gonna be gargantuan problems. Bomies sit whenever they go over certain tiles, but what if the tileset maker was careless and made those indexes refer to, say, flowers? The whole thing would be messed up. Similarly, things like my dream sequence wouldn't work and a multitude of stuff like that.
It'll only be viable if people merely edit the normal tiles but is that really gonna happen? No, people are going to get adventurous...