Some other private servers with low population have implemented mercenary mode so that, if there are 15 alliance and 5 horde in queue, a 10 man bg will pop with 5 of the ally playing as horde.

I hope they try that for Neltharion during long queue times. I agree it's not ideal to have people playing other factions, but anyone who has done rbgs will tell you that they get assigned to play the other faction all the time and no one cares. It's just like "oh, we're alliance this game"- something you take note of but don't really care about.