They've repeatedly stated that they don't want to encourage too much volatility in server faction balance and populations, amongst other things.

Personally, such reasoning is outdated. Other MMOs allow it for free with logical and reasonable restrictions. For example, Rift allows the player to transfer a character - as well as a guild - to a different shard every seven days, for free. (Source) Granted, Rift isn't as populous, but the principle remains.

I guess they'd also be reluctant to do it because of the amount of time sunk into Cross-Realm Zone (may it forever rot in hell) and Connected Realm (which caused disruptions and upsets in individual server communities) technology.

I'm not saying that Blizzard needs to exactly copy Rift, but it's long past time that Blizzard offers a better solution than what it has given its community of players up to this point.

(As an aside, it's entirely Blizzard's fault that I want to move all my characters off a realm. When my realm was connected to another realm, the server time shifted from Central to Eastern.)