So, when building a staircase, I wanted slab stairs, with a wall (vertical slab) on the outside to give a bit of a low railing feel. The trouble is that I can only use the wall that way every other stair (e.g. when it’s a bottom slab).
As a crazy person, I’d love to have quarter slabs, so that I can stack 'em to make a vertical wall that matches.
But, a more interesting (and far more flexible) idea here would be to have a square chisel which lets you carve out corners as cubes rather than slopes. This would allow us to make all sorts of fancy shapes. Like upside down stair blocks, corner stair blocks, dirt steps, corner trimming, etc, etc!
It would definitely let you get around all the block placement magic that other games do (for example how Minecraft joins stairs into a corner piece)
Hell, could even get rid of the wall, slab, and stair types that way and just have players chisel regular blocks to make them. That might be too annoying, though.