Like tabs so many years ago, it's the kind of feature that seems obvious in retrospect. I can't think of a hard technical reason why we couldn't have had container tabs a long time ago. I hope mobile and desktop OSes will one day implement the same feature for apps/programs.
Whoever was involved in coming up with the idea and with implementing it, thank you!
I wonder if there are any plans to make the UX feel simpler and less crowded…