Security of the client and global interest is my main concern. Of course, the 3.X client is much better since the engine is polished , and WOW TBC Gold tools are much easier to utilize. However, I feel I've lost this Vanilla aspect to switch from 2.X to 3.X.X and I'm not keen on releasing WOTLK content. It's unclear if there is anyone who would like to play on a customized 2.4.3 server.
There are plenty of custom server launches, and their popularity never declines. My opinion is that they are launched with little content. If a server just announced itself after doing the effort first: here's an modified version of tbc that has all these additional dungeons, raids housing etc, I'm confident there would be cheap WOW TBC Classic Gold a big audience.