I doubt it'll make a difference. You can already specify "no doubles" in the group description or lock the last few spots to specific roles.

I always found "no doubles" amusing in EX groups though. These groups, without fail, never take advantage of their earlier LB3. They just save it for the healer and melee lb at >10% like everyone else. It feels like they're just repeating something they saw a Savage progression group mention, in the assumption it's more "pro", without even knowing how it works.