Twisted Treeline for me, is like an alternative ARAM. You get to play whatever you want, whatever lane you want, as long as your intentions aren't remotely close to feeding/trolling, which rarely happens in this game mode anyways.
Why resort straight up to removing TT?? Why not make some balance changes (like the funneling strategy) and see how it works out? Maybe give it a slight update?? Just because the numbers are small when it comes to the playerbase, doesn't mean it isn't worthy of staying in League.