Jeremy Ernst, Director of Technical Art on Project L at Riot Games, published a LinkedIn post that states the company is looking for an experienced rigger who could both review the external work done for the project by the partners and do some rigging work on the game. The developers are aiming to fill this position as soon as possible with a set of prerequisite qualifications and responsibilities.
This could indicate that the company is currently working on character-rigging and animations, meaning that the game roster is in full works.