The irony is that you’ve almost perfectly described our guild’s policy. We recruit classes, not specs. If you are a class that can heal, then you are expected to come as a healer (except for one dedicated feral tank). However, we will have more healers than we need, generally, so the healers will be able to rotate out as meme specs.
But those are considered as off-spec, not main-spec, with regards to loot privileges.