Another option I suppose is to template the characters (you start at 58 like they said), and give it several weeks before the dark portal opens. This would allow horde and alliance to level paladins/shaman to max, without feeling the pressure to 'catch' up like they did when TBC launched so many years ago. It's not authentic, but it doesn't have to be. This is a pretty simple solution for them, and if they only allowed you to have say three characters created at a time (for launch anyway), it would be way easier to figure out how many servers they need. That's if they feel that the economic burden of having people jump into TBC with tens of thousands of gold would be too much, otherwise just let us copy each character over 'x' level once.
It seems obvious to me they don't want to disrupt classic too much (but just having your 60 vanish forever) and of all of those options, resetting everybody at level 1 would be a huge turnoff for most people. If people want to play TBC, they want to play TBC, and I'm sorry, but at that stage most aren't really interested in leveling in the old world anymore (it exists, in it's prime on classic servers now). The focus should be on TBC and the options should be anything that easily transitions our characters into those servers, whether it be copies or templates.
I said it earlier they really need to space out raid content. TBC had such a massive amount of shit to do at the beginning, followed by a long period of nothing once we hit Black Temple. I would actually prefer if SSC/TK were left out (especially Hyjal) from launch content and released a few months after TBC launched. Not a huge deal of course, but if they actually follow the timeline of TBC and leave Black Temple as the only real content for that amount of time to make it authentic, I'd be pretty disappointed.
There should be changes though and people are absurd to think otherwise honestly. Natural progression would mean destroying classic servers as we naturally progressed from vanilla to TBC 15 years ago. There would be such an uproar and a massive amount of crying if they converted every classic server to TBC, and they aren't stupid enough to do that. If population dwindles on classic servers they can just merge them together to make server communities healthy.