Yes, sooo much time, anything could happen between now and Spring even.
But going off current, making the assumption Gray will only keep getting more consistent, then yes, he is the clear absolute starter Day 1 come next year. The thing about Kill is, I'm not sure if that will mean an automatic redshirt for Nelson. If he feels he is physically ready and is beating out Shortell, he may give him some minutes next year, and then say, "alright, next three years are all yours Philip". I don't know how Kill feels about redshirting guys and then bringing them out to start as redshirt freshmen without any experience at all. He may be completely cool with it, but he seems to value experience so just throwing that out there.
Shortell seems to be that guy in the middle, who may improve enough to become a guy who can run this offense well enough despite not being a "mobile" QB, and if Kill feels that he can be the guy for at least the next couple years after Gray, then yeah, I definitely see a Nelson RS coming with a competition then occurring the year after Gray.