Concrete is shaping up to be the new generic building block in the game.
This addition would probably make even redstoners switch to concrete for wire tracing, since one-way slabs can be colored.
Oh and I also basically need it for a certain park
EXTREMELY DIFFICULT (if not impossible)
it's possible to make a falling sand object that looks like a shifted block, which if you block view from below and sides could look like a halfslab.
This is laggy, might dither, needs extra steps (like a boat) to get a hitbox, and are not true slabs.
With a resource-pack it might be possible to fake the half-slab texture to look good from all sides as well, then the datapack would only need to set up the collissions