I was intensely interested in this, and after much reading, here's my best understanding:

Neither Brave nor Vivaldi are proposing to maintain engine support for v2: they both point to the codebase retaining support after Chrome drops support (likely for enterprise) as being the driver of their ability to offer v2. Both say that once those codepaths are removed, so too will v2 support be removed from Vivaldi and Brave.

No idea when Google will make that call.