Many people find themselves in bad situations with alts and friends not being able to play on their server due to how suddenly the locks were implemented. Please consider a brief “transfer window” to allow people to get their character roster and friends together on these servers this week. You can lock the servers again in a few days or whatever. This will allow people who are active now a chance to make final preparations for the expansion launch. New players will still have to find servers that are less full when the queues start but I feel really casual players will only start playing when the actual expansion launches.
Or, at the very least, do what many have suggested and let players with active characters on the locked servers be able to transfer their other characters to the locked realms. This could at least solve the “alts are stuck on other realm” problem.