I actually wonder if Kizaru will actually betray the Gorosei or possibly even play the role of villain because he believes he is too far gone.
Part of me wonders if the latter is possible because if youve killed your friend for people you potentially hate, it might just end up breaking you to the point of no return.
Ultimately i have no idea, but if Luffy had to beat SOMEONE this arc, it still should be Kizaru.