Yo Mdrachet5 we'd like to keep speedrun.com Single Segment but we have this site:

http://www.soniccenter.org/

It has all sonic games and leaderboards for all kinds of ILs From Time Attack to Ring Attacking to specific categories depending on the game.

I recommend you going there if you are interested in ILs. If the mods of the Sonic Series change our mind and we include ILs for the games i will post here again or we'll make it somehow for everyoen to know.