I think that if/when BC happens, it should be handled in a way that might make your questions irrelevant lol (no offense!). Here’s what I hope they do:
Make new servers that are specifically TBC versions of their parent servers. If you played Classic on Grobbulus, there is now a new server called Grobbulus-TBC; These servers would be separate from their ‘parent’ servers, in that Grobbulus players would still be playing an unaltered, Classic 1.12 build of WoW, BUT they would have the option to copy ONE of their characters–with maybe no more than 500g–to the new, Grobbulus-BC server. This way, players can’t just migrate all of their characters or all of their fortunes made from Classic to the fresh TBC server, and would start on a semi-fresh server, with a semi-fresh economy and a TBC-ready version of their chosen character.
That is what I want to see happen. So, opening up belf/draenei character creation early stops being a thing, because in my preferred execution of TBC Classic there is no early character creation…just new servers.