It's an interesting topic I think even though nobody can ever answer it. Personally I have my doubts, I think broad concepts such as symmetry tended to matter more to Jobs. He was also very keen to maintain the user experience across devices and, due to the notch, certain aspects of the UI will be different on the X.
The only thing I feel confident saying Jobs would not have accepted would be a situation with so many different iPhones on offer. The SE, 6s, 7, 8 and X (and the 6s, 7 and 8 all having a normal and a plus sized model) must be confusing to those who aren't avid tech followers like most on here.
It's very hard for a CEO to avoid this. You have marketing people who tell you this or that segment want to spend precisely $550, you have engineers desperate to push whatever creation they were involved with, you have supply chain guys telling you about production lines that might as well be used. It's very seductive which is why it nearly always happens with nearly all companies; sooner or later they lose focus. Jobs on his return to Apple really had to battle the engineers there, men he really respected and loved, because - like many on this board - they love the technology but don't see it from the point of view of the ordinary person.
Would Jobs have insisted on there being just one iPhone at a time in one size? Probably not. But no way he would have accepted the current line up of EIGHT different iPhones, some separated by just $40 or $50 from the next one, some being confusing such as a 7 plus 128gb costing more than an 8 64gb - it really must be a bit unsettling for many average consumers I think.
Jobs used to insist apple computers went into one of four categories - amateur laptop, amateur desktop, professional laptop, professional desktop. I suspect he would do something similar with iPhones - a simpler device in large and normal and then a higher cost device in large and normal. And that would be it.