Tab trees would be pretty cool, especially if you list tabs in column view like I do. Opening a link in a new tab would list as a child tab, and the list of child tabs could be collapsed/hidden. Drag child tabs out of the tree to become parents themselves.

This would be great for dynamic research tasks. You could collapse trees and get a top level view, useful if you're in the weeds; you could close trees by parent, great for killing avenues of research you no long need. It would also be good for when you need to quickly check the syntax of something or fix a minor bug without disrupting the larger project you're focusing on.

From a Dev/LiveOps perspective, it would be huge- grouping all my AWS pages, CMS pages, custom dashboards, would be a huge help. I can easily sprawl tens of separate tabs to get different services to talk to eachother.