>>27135550I'm sorry anon, but I bet that's exactly what's going to happen.
He wins, ditches his friends and pokémon, moves on to Alola and starts everything again. The only difference is that from now on he'll probably win leagues regularly and challenge the Elite Four and Champions.
There's a reason they never specified what a Pokémon Master was. With a goal so vague, they can recycle the same protagonist virtually forever.