Consider a feature from earlier in the keynote: the thing Notes (and Math Notes) does now where it fixes up your handwriting into a facsimile of your handwriting, with the resulting letters then acting semantically as text (snapping to a baseline grid; being reflowable; being interpretable as math equations) but still having the kind of long-distance context-dependent variations that can't be accomplished by just generating a "handwriting font" with glyph variations selected by ligature.
They didn't say that this is an "AI thing", but I can't honestly see how else you'd do it other than by fine-tuning a vision model on the user's own handwriting.
Well, here's another one: they promised that your local (non-iCloud) photos don't leave the device. Yet they will now — among many other things they mentioned doing with your photos — allow you to generate "Memoji" that look like the people in your photos. Which includes the non-iCloud photos.
I can't picture any way to use a RAG to do that.
I can picture a way to do that that doesn't involve any model fine-tuning, but it'd be pretty ridiculous, and the results would probably not be very good either. (Load a static image2text LoRA tuned to describe the subjects of photos; run that once over each photo as it's imported/taken, and save the resulting descriptions. Later, whenever a photo is classified as a particular subject, load up a static LLM fine-tune that summarizes down all the descriptions of photos classified as subject X so far, into a single description of the platonic ideal of subject X's appearance. Finally, when asked for a "memoji", load up a static "memoji" diffusion LoRA, and prompt it with the that subject-platonic-appearance description.)
But really, isn't it easier to just fine-tune a regular diffusion base-model — one that's been pre-trained on photos of people — by feeding it your photos and their corresponding metadata (incl. the names of subjects in each photo); and then load up that LoRA and the (static) memoji-style LoRA, and prompt the model with those same people's names plus the "memoji" DreamBooth-keyword?
(Okay, admittedly, you don't need to do this with a locally-trained LoRA. You could also do it by activating the static memoji-style LoRA, and then training to produce a textual-inversion embedding that locates the subject in the memoji LoRA's latent space. But the "hard part" of that is still the training, and it's just as costly!)
That's going to be something similar to IPAdapter FaceID: https://ipadapterfaceid.com
Basically you use a facial structure representation that you'd use for face recognition (which of course Apple already compute on all your photos) together with some additional feature representations to guide the image generation.
No need for additional fine-tuning. A similar approach could likely be used for handwriting generation.
I believe this could be achieved by providing a seed image to the diffusion model and generating memoji based on it. This way fine tuning isn't required.
They didn't say that this is an "AI thing", but I can't honestly see how else you'd do it other than by fine-tuning a vision model on the user's own handwriting.