When Twisted Treeline is gone, that means among other things...
Face of the Mountain will be basically removed from the game.
New players won't have a place to practice champions while only having to worry about learning 6 champions in one game, instead of 10! 10 champions from 6 is a 66 percent increase in things to learn.
Maybe they should bring us a 2 vs 2 mode, since 3 vs 3 was so unpopular.