In it 2016 season update, Riot Games said that it will begin testing the client in early 2016 with plans to roll it out later that year. The new client will be more responsive, easier for the studio to work with, and both streamlined and visually consistent. Only 30 players will be selected to test the initial alpha client, so if you sign up… good luck with that.
Riot said that it’s also working on ways to give players more social tools: “We’re already working on quite a few features that will make playing with friends easier, including parties, clubs, and the friends mobile app. The updated client takes that goal further by giving you a resource-light, standalone friends list you can use to stay in the loop without needing to open the full-size client.”