It’ll be good to have a feature to stack the open tabs, based on their hosts. This feature will be particularly useful for researchers, developers, nerds & students, who often open too many sites at the same time.
Also, I believe it is a must have feature that let’s users to hibernate the background tabs - blocking network to those tabs other than the current tab. The target audience will be the same as above.
I have used both the features in Vivaldi & found them very useful - esp. the background tabs hibernation. It saves lot of bandwidth. I believe Slimjet has it too, just implemented in a different way. This will definitely be a key feature, when it comes to choosing between diff. browsers.