Just a slight productivity hack here could be a nice feature.
I’m assuming people often have a number of brave windows open each having a number of websites of similar topics grouped in each window.
It would be cool to have a small flag/bar that you can apply to a window to label it. (Work, bike shopping, side project).
Most likely with a unique color so you can quickly identify that group even when its minimized in the mac doc menu on the bottom or stuck behind other windows.
Bonus points if you can get the menu hover tool tip to read the name of the grouping.
Just a thought - have a good one!