I have few ideas. Why can't people create their own filter bubbles? Lists do that in some sense. How about "For You" tab but for a particular List so that recommendations expand and let me get the feel of that particular List's filter bubble. Why can't I choose to browse Twitter as it appears to a particular category of people e.g. say a mathematician or neuroscientist? Twitter is all public, there is no fear of de-anonymizing anyone if Twitter decides to implement such a feature.

I have a similar line of thinking. However I think it applies generally and that any "broker" (e.g. Amazon) that is not explicitely on your side will be in conflict of interest. The implications are actually deep and wide.

> There are online communities beyond X

As an aside, I find this phrase funny today. In the past, I would have known you are using the term 'X' to be a generic reference to online communities. Today, I don't know if you are talking specifically about twitter or just a generic online community.

People don't seek maximum diversity. People seek the exact diversity of a small sample of the world they tolerate.

The people that say they do are just unaware of all the diversity they reject.

You mean you don't follow random topics you don't understand or like? :)