Brave must be about cutting-edge innovation to add followers. Your early adopters are obviously power users and Brave must attract them, so be ‘brave’ and don’t shy off from adding powerful features.
I propose vertical tabs.
Tree tabs in general are the future for landscape monitors, they optimize vertical space and organize content.
Vivaldi i.e. has native vertical tabs, but it can also support kroppy’s excellent “Tree Tabs” extension.
Brave could implement a native vertical tab feature and at the same time give extensions devs APIs powerful enough to implement something like Tree Tabs as an extension.
To implement a native feature we can study the best existing extensions: “Tree Style Tab” on FF by Piro, “Tree Tabs” on FF by kroppy and “Sidewise” on Chrome by Joel Thornton.
Tree Tabs example on Vivaldi: