> I'm talking about websites that function like apps but have the privacy/security benefits of being sandboxed inside the browser (accessed by URL or link).

What privacy benefits are not being realized by the current approach? If I want privacy, I can just disable JS for not letting some website know too much about my device. But in general, privacy is a joke since Edward Snowden's revelations.

> I'm advocating for more capable websites (which IMO "ought" to protect user data--not leverage it).

What opportunities are not being realized with the current approach? Who will be responsible for protecting user data, given that every website/resource/service strives to sell Alphabet/Meta as much data about you as possible.