Brave actually doesn’t take all of Chromium’s new code. They write patches that modify what gets brought in or used, which allows them to avoid bringing in changes they don’t like.

More info here: https://support.brave.com/hc/en-us/articles/10742158329613-What-does-Brave-remove-from-the-Chromium-engine-

See also https://github.com/brave/brave-browser/wiki/Patching-Chromium

I don’t know how extensive Brave’s changes are, but it would definitely be easy for them to add their own ad blocker. On the other hand, changes like re-enabling the entire APIs that were taken away from extensions would likely be out of scope.

It’s an interesting process but I’d personally rather just use Firefox