Quark has this feature that allows panes, walls, etc to connect to their vertical slabs, they also allow this feature to be extended to any vslab by adding them to the quark:vertical_slabs tag, problem is:

1. you need to have the quark vslabs enabled for this (just jei clutter if you have this mod)
2. adding any tag from this mod (like #additionalplacements:minecraft/vertical_slabs) to quark's tag makes the server do a perpetual loop of what it looks like a recursive tag addition (AP trying to add the one tag to the other and loops?)
3. even adding the AP tag to the quark tag I don't know if it works (because 2)

would also be nice if this extended to vertical(?) stairs

You can fix numbers 2 and 3 by disabling automatic tag generation and just running it once yourself.

I would like that