Vivaldi is about to drop support for Manifest V2 as well:

https://www.reddit.com/r/vivaldibrowser/comments/1urieed/com...

I'd been using it solely for GMail / Google Drive / etc. at work, for whatever improved compatibility a Chromium browser might provide over Firefox, which I use for everything else. I got the warning that UBlock Origin won't work, and I immediately ditched Vivaldi. I'm sad about it, I think Vivaldi otherwise is a good browser.