This restriction made very little sense back when people actually levelled in the open world, it makes even less sense now when you can skip 80% of the levelling with a character boost.
The old world is a ghost town and most players don’t care where you levelled (aside from a handful of bads who feel its some sort of an achievement to level on pvp). Right now there are single faction “pvp” servers you can level on and transfer to a balanced pvp server… but if you made a mistake moving a character to pve without realizing its irreversible, well thats it… You are stuck there permanently.
I made a centralized thread so we can get the attention of Blizz devs to hopefully implement this as soon as next Tuesday. Please upvote/share/comment here to help get this post trending for attention.