I dkdn't know if Oda had that in mind at the time, but anyway Doflamingo has a long history of selling Law short.
Imho, a D., most flashed out WG member, fan favorite, basically guaranteed to have a big role EoS with a dream related to the Void Century, ecc...
I think Law having CoC Is very likely. Not as likely as, idk, Sabo, but still very likely.