However, one thing that could be done is integrate uBlock into a chromium based browser. The removal of manifest v3 would still be painful, but uBlock would survive and we get a browser with exceptional ad blocking capabilities builtin
Rather than hardcode one extension in, re-open the gate to privacy protecting extensions having a lot of tools at their disposal.
There's nothing to stop other people from making specs! The main barrier is that there's such a a limited pool of people willing to go implement.
My suggestion was to get a new browser up and running with good quality ad blocking
Or include it in MV3. Firefox's implementation for MV3 avoids this problem almost entirely by just not getting rid of the specification and integrating it into the new system.
There are technical problems with MV3 in Firefox (it's extraordinarily buggy right now), but my suspicion is that by the time it matures it will be a straight-up improvement over MV2 for both privacy and capability (especially if Firefox ever gets around to supporting extension service workers).
It's not really MV3 that's the problem, it's specifically Google's implementation of it and which APIs they've chosen not to include.
The downside for other browsers based on Chromium is that even if they go Firefox's route, they're all largely dependent on the Chrome web store for extensions, and I think it's unlikely that most extension developers continue to develop Chromium extensions that don't work in Chrome.