I think if a bunch of Chromium forks come together, they can maintain v2 support for quite a while. A fork maintained by a combination of Brave, Opera, Vivaldi, and maybe some of those startup-based browsers can probably keep the most important APIs running for quite some time.

At some point the issues will become too difficult to fix, but none of these companies need to be doing it alone. Adding a separate upstream with some "fuck off Google" fixes for them to base their proprietary browser on seems like a smart thing to do.