Guests Characters in LoL
Since league is currently "The biggest online game ever", Riot could be in a good position to reach out and try to get some Guest Characters for their game. Other big-name devs are grabbing guest characters and it helps drive interest in the games or create bridges between communities (Killer Instinct, Mortal Kombat, Street Fighter and Namco).
So what's stopping us from seeing Cloud or Mega Man in League of Legends? Or even Riot's iteration of a DotA 2 character, or a Smite god?