I think you are spot on, and this fits perfectly within my mental model of HomeKit; tasks are distributed to various devices within the network based on capabilities and authentication, and given a very fast bus Apple can scale the heck out of this.

Consumers generally have far more compute than they think; it's just all distributed across devices and hard to utilize effectively over unreliable interfaces (e.g. Wi-Fi). If Apple (or anyone, really) could figure out a way to utilize that at modern scales, I wager privacy-conscious consumers would gladly trade some latency in responses in favor of superior overall model performance - heck, branding it as "deep thinking" might even pull more customers in via marketing alone ("thinks longer, for better results" or some vaguely-not-suable marketing slogan). It could even be made into an API for things like batch image or video rendering, but without the hassle of setting up an app-specific render farm.

There's definitely something there, but Apple's really the only player setup to capitalize on it via their halo effect with devices and operating systems. Everyone else is too fragmented to make it happen.