I am also reading the long 20th century. Haven't gotten that deep in it yet, but yeah, China does seem poised to become the new and final hegemon, given the historical trend of each capitalist hegemon being larger than the previous one.
I do kind of expect the book's analysis to be of limited quality, since they seem to be working off a bizarre and unmaterialistic definition of capitalism based on political power and commerce (a pre-marxist understanding). Maybe as I read along it will be cleared up.