Basically default mode should decruftify all the websites you visit. Destroy all the known garbage on websites that doesn't serve browsing expeirience just tracking and advertising.

Have an easily accessible slider to adjust level of this intervention for current website so you can turn all the crap back on if site doesn't work or complains, or disable event more (javascript, decorative styles).

I'd be also happy if they provided additional tools for modifying the way content is presented, for example influencing order of repeating element like table rows and other. Filtering. Site specific bookmarking. Linking to specific positions in the document. Highlighting.

It should bring back the control to the user and give the users more control they ever had