I'm not sure I follow you. The Coliseum itself would consist of all of the sub forums, if that's what you're asking by "what would go here?".
so you're asking for the coliseum to not be a forum anymore (since nothing would go here), you basically want forums for every sport - they wouldn't be subfoums. no one would need to post here if there is a forum for every sport, that's not conducive to how this board works. i could see if this place had 20,000 users or some shyt, but it doesn't
current format
Main: Coli (every sport)
Sub - Th ring (wresting)
Sub - Fantasy
etc.
You just proposed
Main: COli
Sub: NFL
Sub: NBA
Sub: MLD
and so on
what would go in the coli? that's pointless, nevermind the fact that you have to click back and forth between hella forums (if not using multiview)