Well, I know you already started and I don't want to break you down, but...
- Clan and Team Management: Most clans already have their own forum which they have been using in the past, and they prefer it that way. People don't need to declare online who is in their team and who isn't, and if they do, they don't need a site for it. They need to reply to the "Clans" sticky on the forums.
- Cup,Ladder Challenge Script: There is already FunWar, ESL, and PSL. Again, people like to stick to one site for content, instead of visiting a couple.
- Challenge function: Challenge script would go into their own forum. It isn't worth visiting two different sites, yours for new challenges and their own for existing challenges, archives of pictures, etc. The transfer time is not good.
- Community features: Probably the only useful part of the site. Go ahead with this if you want.
Recently a lot of people want to create their own community, but it doesn't have any real additional functionality. If you are an uber-1337 programmer, look into an XML reader that can read .DEMO files online. That would be awesome but almost impossible. What really needs to happen is for the official teeworlds site to become more of a community than just a forum.
If you still want to go ahead with this plan, I'd love to be a beta tester.
<? php echo "Magix"; ?>
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Tee-City <--------- The one Teeworlds site to rule them all!