Yes, but seems like a lot of hassle for not much gain (for Google).

The gain, as far as local AI goes for Google, is that, at Google scale, the CPU/GPU time to run even a small model like Gemma will add up across Gmail's millions of users. If clients have the hardware for it (which Pixel 9's have) it means Gmail's servers aren't burning CPU/GPU time on it.

As far as how Gmail's existing offline mode works, I don't know.