While I don't see MS sticking with a number scheme, if they were to stay that course then,
Xbox One Sc (c model like apple, also short form for Scorpio)
Xbox One SE (another apple name, like c and pro)
Xbox 540 (follows the 360 train of thought, and also sounds slightly better/ahead of PS4/PS5) Xbox 1080 (follows 360 again, but also fits with Windows 10)