I like the concept behind the tileset 1 type that lets you place things into blocks, but I'd love it could be taken a step farther and I could define blocking tiles MYSELF whether by script or what.
I would love if I could just have a tree image, put it where I want, and be able to assign the tiles a block or dontblock myself.
And I would love if the original tileset structure would allow me to place competent buildings into the tileset so it makes sense.