Well, I think the problem -most- people have, is accidently killing their group mates. In the past if it wasn't a typo, it was an area attack hitting group mates and mass melee ensuing. So that's the -real- problem. Odds are -very- low of say, me and Belrath being in the same room in different groups, and one of us accidently attacking the other while trying to hit a mob. They exist, but... c'mon.
So the solution is simple! ... at least from my perspective. Alter the logic so it prevents you from attacking group mates. Use the sort of logic that's on pets. You're not allowed to attack other players pets, so the code already exists... in a sense. The only matter would be adapting that to check for them being a part of the same group as you, and yada yada yada. I'm not good at C... hell, I can barely understand what some of it says, let alone actually code a line of text.
But the nitty gritty of the problem is accidental attacks on groupmates. Eh, 'bout all I have to offer... and I know it's been brought up time and time again in the past.