I often wake up screaming and in a cold sweat after dreams of working on more Warcraft III stuff.
But seriously, it could certainly be done, but would require a huge amount of work to do well or even competently, and I really don't want to dedicate the amount of time it would take to make something like that. I'd much rather work on other projects at the moment (and also play games that I've owned for literally years and never had the time to play... like Baldur's Gate).
I have toyed with the idea of a multiplayer hero arena type map (similar to Chapter VII) using characters from TTBE, but even that would be tough. I have no experience making multiplayer maps to start with, not to mention that since it was single player, TTBE's heroes never really had to be balanced. It would require more than a little tweaking to do even that.