I haven't seen this yet... anywhere... so here it goes.
There are a lot of websites with competition and a ladder is a must. The site that I am going to use as an example is
www.GameBattles.com. The ladders on the site are completely custom made by the owner, but it's got the same idea. Having a built-in ladder system would be one of the best hacks ever made.
Allow for clans, single player, game selections, wins/losses, matches (agree to, decline, etc), rankings, activity, etc. Run through GameBattles' ladder system to see how it's all setup. Then a tournament would be nice as well.
I know there are a lot of sites that would absolutely kill for a hack like this. Hell, I'd even make a hefty donation to the creator(s) of this hack.
Let me know what everyone thinks. I know this would be a difficult one to make, but I know it'd be well worth it.