Fixing imbalance by adding more imbalance can only harm the game, because now, the majority community is left behind and would cry aboot such things, rightfully so.
And assuming they’re not, I’m not sure that would be enough to move a well established community to the other side. The roots are so deep that moving such tree would only kill once and for all said tree.
If someone from the alliance wants to play on the horde, they can reroll. Faction transfer should serve to enhance faction balance and nothing else. If the players are a concern… then we really don’t have any trouble. Just everyone swaps to horde and bam, everything’s fixed.
Is it the same effort, though? Or does having 1/10th (and yes, that’s the disparity at least at endgame) of the population make the effort actually much greater, which warrants the extra reward.
My suggestions are much, much simpler than making the game an absolute inconsistent mess that makes no sense in the narrative sense and in the gameplay sense.
I demand that the game make sense. If you can party with someone, you should be able to walk up to them. It’s kinda that simple.