Currently Botania uses over 100 ids alone on stairs and slabs, which cannot be disabled, its a pretty easy fix, and would be useful for people who have mods such as Carpenter's Blocks which allows any block as a stair or slab

Or can the stairs and slabs be the same ID, but with metadata?

Stairs cannot due to how stairs use metadata to store rotation. Slabs could be compressed a little I suppose

Slabs are used for recipes, so this would be one hell of a mess to make. Putting it on the backburner.