It seems as if they will track it (https://brave.com/blog/brave-shields-manifest-v3/), with an exception for a selected few extensions (AdGuard AdBlocker, NoScript, uBlock Origin, and uMatrix).

The few exceptions being the ones we want. So.. a good outcome.

We want forks or better extensions impossible?

If they were willing to make exceptions then I would hope the list isn't closed. I view this as the best of the possible worlds not the best of all imaginable worlds.

Perhaps good was overkill. Less bad?

They would add the most popular fork if uBlock Origin was abandoned is plausible. They would add a no reputation developer's proof of concept is unlikely I think.