I think that would work well. To that, they could just limit the amount of premade groups that get into the same epic bg. For 10 and 15 man bgs, they could limit them to a max of one group of 5.
Basically, if you want to queue with a group, you might have a very slight increase in queue times.
I remember that. There was a lot of weird stuff like that. While there were no shortage of guilds doing shady stuff, I recall some getting stopped from the world first chances because they came across a bug that they didn’t know was a bug.