I've just tried "sponge:2" with 1.7.10 and it has no problems whatsoever with it, so we could use that.
Unfortunately, I think the blocktype merger has to work even when it's called for areas without metas, so it will still consider all the sponges as the NOP block. I guess that's good enough for me.
Unfortunately, I think the blocktype merger has to work even when it's called for areas without metas, so it will still consider all the sponges as the NOP block. I guess that's good enough for me.