Lol yeah leewaihom, at a matter of fact, the idea of two RL in a raid is nice, but I've seen so many stories about people not agreeing on the strats and just wasting a raid night caus of ego, it kinda marked me for the rest of my days.
That being said if peoples can manage to make a guild horde side on a pvp realm(caus transfer from pvp to pve aren't allowed as far as I know)I wouldn't mind transfer one of my chars to give it a try, for sure.
So far mixed guild can work well, but their biggest problem are that they rely a lot on their RL, if one cannot come, sorry no raid, or if one decide to quit, to move, to leave the guild, or to spread the *sheet*, same result.