The forward march of Apple stripping away UI elements continues. Some quite bad tab-related ideas in there, and an excellent point on tab grouping:
A little experiment: how many browser tabs do you have currently open? Let’s be conservative. Let’s say nine. How many are so tightly related among one another that you can meaningfully group them together? I bet none to very few.
If I am working on something with a bunch of related tabs, I am more likely to have a dedicated browser, or user, or session with those. I don't want to juggle and maintain tab groups to deal with their agressive UI culling.