I have looked into it again — as far as I can tell there is nothing keeping Apple from the Photonic Engine on the iPhone 13 Pro on a hardware level. Well, anything is possible, even something like what you describe that could be part of the new Pro’s ISP, for instance, but the ISP itself is part of the A15.

So it makes no sense to change the whole SoC for a specific block, certainly not from a manufacturing standpoint. I am 99.9% certain it’s a software matter and that is why I consider this to be an issue.

You are right, they have backported new features to older devices in the past, but it’s a rare occurrence and, almost every time, not something important or something that could be used as a marketing bullet point.

Apple usually backports something if it wants it to be widely used. If it can work as a reason to sell more devices, it will choose the latter. That’s been my view of the company’s choices so far.