To be honest I would enjoy old versions of the game more then any kind of Urf.
URF exemplifies the balance issues league still faces on much grander scale and in turn a meta is formed that does not even really allow for the existence of one trick ponies of non meta champs.
And people who don't get a spam champ often rage about not getting to pick who they want with ARURF.
Perhaps if URF was properly balanced on an individual champ basis it would be more enjoyable but It is not intended to be the core of LoL. It is a rotating game mode and there are better things for riot to be focusing their efforts on.
I would much rather see Riot put past versions of the game as rotating game modes then urf at this point. Be it season 1 worlds patch, season 2 worlds patch, League of Cleavers (V1.0.0.152) just to make people see how bad it was, 4.11, 3.7 or the patch right before the Juggernaut update. Heck put alpha/beta versions of the game on just to show how far the game really has come. That would be far more useful for Riot to gather information on what has been happening in the game over the years while also allowing newer players to experience what older players often talk about.
There would not be any balancing needed for this kind of game mode (unless something game braking happened) since it would be a functional older versions of the game as it was and only for a weekend here and there.
And yes I do believe that these rotating game modes would be popular if not overdone.
We know you have functioning old patches of the game which was confirmed to find out when the Riven CC canceling could first be done. It would effectively be making use of outdated work to add something to the game that many players would likely enjoy.
EDIT: for those who fail to consider the difference between this suggestion and doombots or Butchers Bridge this would be playing on an old version of the game and not trying to put old things in the current version of the game.
