Given that Nocturne was in one of Lux's short stories (it's a given that it's him), and given the new Evelynn backstory, I think it's a safe assumption that Nocturne will be among the Demon Champions.
Though Noc seems to be better than Eve at making people suffer though. He can easily turn a town while eve has to hunt people indiviually.
Not even a theory, with how riot is doing things typically in a lazy fashion.
Hopefully they don't just shoehorn fiddlesticks into demons do to laziness.
Nocturne resides in the realm of dreams , nightmares and terror.
I doubt he become a demon, but it's a fair guess
His improved identity in Lux's lore was more about him being a living nightmare
