A powerful browser could work, e.g, as the basis for any type of local-first application and we would solve 98% of the issues of social media networks by letting the browser in control of the functionality. [0] We have web browsers that can let you browse through Tor and we would get rid of data tracking. We can have a "good guy's version" of HolaVPN where people could still cooperate in the data proxying, but without the data selling part. Brave gets a lot of shit because of their crypto stuff, but if more people were seriously looking at their platform as a privacy-preserving opt-in monetization platform, we would be a far better place that we are nowadays.
We can not do any of that with an user agent that can do nothing but fetch and present text documents. We need an actual application platform.
[0]: https://raphael.lullis.net/a-plan-for-social-media-less-fedi...