Sinner and Rune are both still highly likely. I probably would take Rune over Sinner, but not by much.
Agreed on Rublev for least likely, but that's not saying much. I feel like Tsitsipas is probably done for with the emergence of Alcaraz and Sinner and Rune (and others) only likely to get better in the years to come.
Zverev would be in the middle of the pack. I do feel like he could still snatch one if he can get back into that zone at the right time. The big difference between him and Tsitsipas is that he's not completely useless in the second half of the year so has 4 chances (well, 3 anyway) to snag one as opposed to 2.