I wonder how much of the image processing Apple could back port to iPhone 8/X, XS, XR if they wanted to? Those phones are extremely powerful still. And Apple has touted the power of their neural engine ever since the 8/X.
For example Portrait Lighting can run on hardware without the neural engine, if you hack the exif to say it was shot on a newer device. However, this is just when editing. There's no way it would be capable of the realtime preview, and casual users rely on the preview to make the feature useful at all.
Actually, it would confuse a ton of users. We added portrait-mode support for non-humans on the iPhone XR. The hardware doesn't provide realtime depth information, so we can only apply the effect after you've taken the photo. We frequently receive support requests telling us that the feature doesn't work.
I can't speak to why Deep Fusion isn't coming to old devices, since it's an offline process. I mean, I could speculate that if it relies on multi-cam capture to capture multiple images, that's strenuous API that isn't supported on hardware earlier than the XS.
The cynical perspective is that Apple caps features to the latest hardware to sell new hardware. I'd say it's just as likely that Apple looks at the new hardware coming down the pipeline and plans features that push the hardware to its limit.
Great, then why doesn’t it work on my XS?
Also, if you're going to share a photo, you're likely going to do it the same day you took it.
About 60-75% of the time I take photos, I share them soon after or within a few hours. Having to wait to let them be processed overnight would be obnoxious.
And it's not particularly helpful to compare people taking photos on their phone to the DSLR world. (Coming from someone with a nikon d200, d300 sitting on his shelf). Totally different use cases, totally different usage expectations.
I know Google made their night model generally available, but I don’t think it depends on specific custom hardware.
I wish they would, but that doesn't fit Apple's typical MO.
Apple, or any business trying to make money?
If anything, it ensured my next phone would be a Samsung again (and it was, I went Note 10), so I think it's still a good upselling move to do so.
On that note, how far they've come since the Note 4 terrible TERRIBLE result in low light, that phone was top notch for its time but in low light it took several seconds for a single shot, focus sucked, grainy as hell ... Seeing a 9/10th gen phone instantly take those shots, with almost no grain and a lot of back details properly lighted is very impressive to me. I understand how it works in theory, but there is still a "wow I can't believe my phone pulls that off" factor for me.
Of course one could argue that the iPhone 8/X, XS, XR buyers did finance the R&D for it. Each year Apple has beat their neural engine drum but it wasn't until this year that they really introduced features that took great advantage of it. Sure, they used it for FaceID, but I'll wager it didn't really tax the silicon much.
Sure it would be nice to get some special new features, but as mentioned, that also doesn't suit how Apple operates when it comes to new features. And that's quite alright.
Android vendors had (have?) a horrible history on this...
My SE has really been struggling with iOS 13. A lot of apps don’t load and things are ssssslow.