At the same time, "GM" is drilled so far into my head that I'd still be using it all of the time. Not to mention, we'd all have to change our names, as most GMs on a server have a GM Title. "GM _____"
So maybe it's just best to stick with what we've already got? I don't think many want to change it, anyway.
I can just imagine announcing to me server "Hey, everyone, from now on we are GAs, not GMs!" I'd probably end up having to go before The Inquisition or something... Just kidding. xD