The really good games are the ones where its almost 1 to 1, tense fights and close wins.
So overall, yes I would like cross faction bgs. If the other team has like 3 shamans, I would like my team to have 3 shamans or 2 and maybe some other strong class in pvp like a rogue. Either way mixed-faction bgs would be very very nice for both factions. Alliance players has a chance of getting more wins than they usually have. And horde players can get faster ques. I think its a win for either faction. They can make it into a “pvp weekend event” and true “Random Battleground”. Where it’ll que you for a random bg alongside a randomized but somewhat balanced faction-less team.
Now the downside. Lore, ego, whatever. Also this is Blizzard. People have been asking for mixed faction bgs on retail for a long time. I quit retail bgs so I don’t know if they do it on there. Also there is the wow community’s commitment to wanting this. I don’t think people really care enough at the moment or at the very least are not vocal enough to want this.