He didn't include Groban because he has some sort of vendetta against Great Comet's producers- he hasn't listed it in any of these articles all season.
I agree that the likely four are Platt, Karl, Groban, and Hyde-Pierce, with the last slot up in the air. Not that I think this will happen, but it'd be funny if Hyde-Pierce managed to win again- the last time he did was against another sure bet.
I am a firm believer in serendipity- all the random pieces coming together in one wonderful moment, when suddenly you see what their purpose was all along.