I'm not sure having one win and one nomination, a decade apart, can qualify an actor as a Tony "darling." I love Mays, but to me Oslo was all about the featured players. Mays and Ehle were narrators and provided the dramatic conceit. I wish they had been offered more to do.
In the original Six Degrees, Courtney B Vance was nominated in Lead. I could see a scenario where Corey Hawkins could break through there as well. John Benjamin Hickey, though wonderful, doesn't have as much weight to his role, comparatively, and I cant see him competing in such a crowded field.
Kline, Glick, and McBurney for sure things. Ruffalo, Hawkins, Arndt, and Mays compete for the last 2 slots.