"An official sequel developed by Valve Corporation was hinted at for many years, and was finally released in October of 2007." -Wikipedia Team Fortress Article
I know I'm a bit late, but I don't think this counts as a dead topic yet. Anyway, I think that it's the same thing with TF3, Kanrik. I mean, it was 11 years between the release of the first two. I wouldn't count on rumors.
Yes, it's certainly worth getting, as it's an amazing game.