Is there anything intrinsically privacy hostile about this potential industry, beyond sending data to a server - which is something you might do if you engage with doctors or therapists virtually?

I hope that consumers choose to pay a premium for privacy preserving services. If users are indeed getting alot of value from the arrangement - I would hope they don't use free or cheap services that need data harvesting as part of the revenue.

My concern is that even premium products would want to pool user interaction logs in order to train better models - which isn't as directly hostile as packaging user labeled data and selling it, but it is a sloppy art to claim you are anonomyizing user data. As any sufficient anonymization necessarily destroys information that would be useful to training.