I don't understand or know alot about extensions, but what is so incredibly impossible about adding new capabilities to manifestv3? It's a manifest describing what the addon wants to do and some UX to allow it right?
And that's a lot of work for a multi million LOC project, unless the architecture is specifically made to support such extensions... which isn't the case here.
And freezing your merges indefinitely isn't really viable either for a browser
That's been the default assumption of pretty much everyone anyway.
If not today maybe soon...
Being independent of google requires actually doing the work and not just copying google.