The kind of Rayman game I'm hoping for is an immersive and mysterious 3D platformer that certainly wouldn't work well for a multiplayer mode. Maybe some multiplayer online minigames could be a nice addition, but the gameplay would have to be very different from that of the main game, unlike Rayman Legends.
In fact, the only games I like playing alone are not games whose gameplay also works online. Resident Evil 5 tried to do both things at the same time and as a result, both modes ended up worse than they could have been as separate things.