So I guess that means that Ryze is now the central character of the game.

I think that out of all the champions, he is the one that have or will have the biggest amount of connexions with other champions. Seriously, who expected him to do stuff with MF or Sona? I feel like the stories will slowly gather around him and eventually the story line will be about getting all the World Runes before the Watchers or Brand or whatever threat that gazes upon Runeterra.