Gosh, this arc actually has tension unlike the previous 5 or so. Every chapter I feel there's less and less chance for the alliance to win.
I still see no way Luffy can beat Kaido 1v1 without any assistance and at the same time Luffy's pride took such a blow with their previous encounter that I don't see him accepting any help either.
Problem is, if he beats Kaido 1v1 completely by himself then that means Luffy automatically becomes the strongest being in the one piece world and future yonko arcs maybe lose hype… Therefore, I don't think he will actually beat Kaido 1v1 (let alone Big Mom as well).
None of the two Yonko will be beaten 1v1, I'm sure. The only UYonko I expect to see defeated 1v1 is Blackbeard, near the end of the story.