How about flanking for advantage, something that is an optional rule for 5e (not the "I get advantage if I'm behind you" backstabbing BS from before, but proper 5e flanking option).
You mean that you should get Advantage on Meele attacks, when anyone else from your party is in meele range from that NPC? That is certainly there, it was dicuised in "Patch 5 news" topic, since Larian removed "auto advantage when attacking from behind" but changed it with this.
No, I mean the way it should actually be implemented. You have to be on opposing sides of the enemy, directly across from each other with the enemy in between you if I remember the rules correctly. Not just "two party members anywhere on one enemy".
