We are working to open our Free Character Move service for select WoW Classic realms in the coming days. When free character moves become available from one of the most highly-populated realms, players will see the option to initialize a free character move on either the character select screen...
The transfers are best taken advantage of by people that are mostly solo and found themselves on a mega pop server by happenstance. Trying to move entire guilds can't be a good idea unless you believe that Whitemane is going to end up low pop after.
Thanks for the answers on the costs of respeccing. Yeah, that is one of the few things about Vanilla that were almost game-breakingly bad. Don't think anyone would have minded a slightly more lenient version of it except from the autistic screeching from only the most hardcore of purists.
You rarely want to move. The majority who transfer off will be loners with no friends or guilds that are very small and often rl pals who can handle it. The big mass of sociable people, who are what you want around to provide pug additions and fill the auction house, are less likely to go. The zerg/blob guilds, who will end up being recruits months from now (or a backup plan if foh goes as well as prior forum interations...) Are the least likely to leave.
It's basically adverse selection, but kinda reverse of it's typical usage. The people who can just drop and transfer are the types you don't want, the folks rigidly committed and not moving you do want to be around.
The exception is if something ON the server was a problem, like if you are on a server where non english all congregated. Then of course bail.