I'm really pleased with that survey.
Few words for devs
For me, as a "tabs manager extension" developer, a very important thing would be to hide tabs bar like I can do in Vivaldi and Firefox (in Firefox it's still not possible from Web extension, but it can be done with XUL, like in "Hide Tabbar" extension, but I know they work on it). https://bugzilla.mozilla.org/show_bug.cgi?id=1208596#
Tabs stacking would be a second thing, especially if tabs could have something like parentId, visible via API for extensions, for example to use native grouping, when you switch between various "tabs manager" extensions, all groups could be the same across all of them. That would be sweeeeet. For now chrome API has only openerTabId, which is lost after browser restart.
I would suggest to contact guys from Vivaldi, maybe you can make a compatible cross platform API for tabs stacking? What you think? Maybe contact Mozilla WebExtensions team as well? You know that Firefox folks made sidepanel API based on yours right?
I'm working on TreeTabs extension for Opera and Vivaldi, after some small adjustments in css it works great in Firefox as well.
Developer's scream: "Unify the Web extensions API"
And btw. As extra widescreens gain more and more popularity, sidebars finally make sense.