It seems like a lot of people want Blizzard to "re-balance" some classes/specs (people that, in my opinion, just don't really want Classic) in the likeness of TBC. And by "re-balancing" they simply mean buffing their dps in raids (which combined with the fact that hybrids were already good in PVP, will ruin PVP).
Now, how they made classes in the Burning Crusade "balanced":
- by adding new talents and abilities like, for example, Vampiric Touch for priest which increased dps and solved mana issues;
- by giving to pure dps classes new PVP abilities to compensate for the increased dps of hybrids;
- they added a ton of class/spec specific gear so hybrids were on the same gear level as others;
- number of debuff slots was increased from 16 to 40, so raid leaders could invite more than 1 sp/boomy/or whatever.
Implementing all these changes in Classic would require a complete redesigning/retuning of all dungeons and raids. And, as a result, we would get a completely different game.
So, if you want classes to be "balanced" like in the Burning Crusade, just ask for the Burning Crusade servers. Leave Classic alone.