My question is, would Sony even be willing to do a SF5 again for a franchise that is in a genre that doesn't do amazing numbers like DMC? I can see them wanting to do some cross-promotion like they did with MonHun, but what does benefit them to pay for exclusivity (and Capcom too for that matter).
For Sony, not much. Especially at this point (late gen).
For Capcom though, there isn't anything to lose, since they probably wouldn't bother making a new one if it wasn't funded by someone else. I mean, DMC hasn't got a brand new entry since 5+ years. If DMC5 is real and succeeds, then Capcom will continue the franchise, probably multiplatform from that point. If not, they will stop making new entries and financially wise it won't be so bad for them, since it was funded by someone else (again, assuming the rumors are true).