Re: #1 I see that as closely related to #4, so see my last paragraph.

To #2, a browser extension to help with this would be great, and wouldn't be hard. I'd expect that to come sooner or later.

I agree re: QT, and some Fediverse software has it already. It's coming.

Ranked/AI managed feeds are very much possible to do with Mastodon/Fediverse. You just can't expect it to get built into the main Mastodon UI. However you could do this w/external software that produces an ActivityPub actor that you can consume either by following it or by adding it to a list. It's on my list (sorry) of things to play with, but I hope someone beats me to it (and frankly, it's a space that's wide open for a variety of variations, going from shared up/downvoting a la reddit, to simple bayesian network over your own activity, to a more complex machine learning model or crazy stuff like asking the openai API questions about whether the content matches whatever profile you want.