A single player mode that follows a champion's lore?

Now I know this is MMO but hear me out...What if there was a mode where you could actually play through a champion's backstory/lore and go through the different levels facing bosses or "doombots" and as you progress your experience on that champion also levels up. Just an idea, I don't really wanna stray too much from the MMO aspect but there's much great lore behind some of these champions that it could make a really great animated series or "story mode"