People always think there’s some ingenious solution to faction balance and population issues, but your plans would all fail. You can’t force people to play a specific faction. If you try to tightly control faction and population all you accomplish is driving people away or preventing friends from playing together.
The best solution for faction balance in WPvP is War Mode shards that automatically balance the numbers of each faction (this also results in overflow shards where some people are basically alone with just their faction since you can’t pull extra people out of thin air if there’s not enough on both sides). You’ll never see that in Classic. On retail they can’t even entice enough Alliance to turn War Mode on with major WQ buffs. You certainly won’t get them to balance out classic servers where they’d have to xfer (potentially cutting them off from one or more friend groups since we have no x-realm grouping) or re-roll for no meaningful incentive at all.
Merc Mode is the best solution to faction BG queue differences, but we’ll also never have that in Classic. In retail even with Merc Mode Horde still have 2x the queue time (though merc mode NPCs are kind of hidden, perhaps if it was built into the UI and more easily accessible they’d be a bit closer).
They stated it before Classic even launched:
Q: Will there be Cross Realm Battlegrounds when those go live?
A: Cross-realm battlegrounds were a feature of 1.12 and are important for matchmaking, so you’ll be seeing cross-realm battlegrounds in WoW Classic when Battlegrounds are introduced in Phase 3 of the content roll-out plan.