Well I don't think this really has to do with Crackdown, I'd argue it more so has to do with the current state of the XONE. MS this gen has made the XONE simply a optional purchase, putting games on PC day and date and even seeking to aim for more devices. Its clear that MS as a whole is done with XB exclusives ie can only be found on XB. I use to think that maybe this was because Win 10, but they started supporting Win 8 and 7, then I thought it was because of the MS OS, but MS started putting some of their games on MAC, then I thought it was the store, but many are on Steam.
Its clear its simply about money as to why at E3 MS was talking about aiming for even more devices like phones, so at this point, I think its a safe guess to say MS might put their games on Nintendo, PS, ios etc in the future.
Never mind just Crackdown, MS in general are basically multiplatform already