I reckon it might be someone who hasn't really made an impact on the scene yet. Reason being is that Phil can realistically go for another four maybe even five years and keep winning as long as he keeps bringing the same size, shape, and conditioning. Remember - Ronnie was a nobody at the '92 Olympia, most didn't even notice he was there. Six years later he was Mr Olympia. No-one would have predicted it.
Kai is too old to win the Olympia and beat Phil and Dexter is even older - even with the best will in the world he'll lose size and shape very soon.
Ramy will never win due to politics, the same way as Nasser was never going to win.
Compton is a gear junkie and will go the same way as Branch and get Palumboism ruling him out.
My choice from the current crop - possibly Dallas McCarver but it's a long shot. Then again, someone's got to win.