Riot has trademarked the name: LEGENDS OF RUNETERRA - League MMO?

I personally don't think it's an MMO, but maybe it's something new and fresh! I'm so freaking hyped right now.

Sources:

Official list (Check bottom):

Reddit post with some insight:

Edit:

And remember, they moved Ghostcrawler to the head of a secret project 3 months ago.

He has a history of MMOs

Again, Im not saying it's an MMO

But I wouldnt be surprised if we're getting something huge

From his offical Boards post:

"We’ve been up front that we want to put the S in Riot Games, and I am helping with that effort. In addition, we have been taking Runeterra as a world more seriously, as you’ve probably realized with the release of the Ryze CG and the world map. While telling stories is really important to us (and I hope many of you), there is a limit to the kinds of stories we can tell in League of Legends without getting in the way of a competitive, multiplayer game. So, many of our stories will have to come through other mediums, and of course that possibly includes other games."