This, of course, is exactly the same model as many pieces of toolbar malware, with the genius addition that by letting publishers opt in to receiving a small fraction of the revenue, they hope to make it easier to accept the loss than to sue.
Of course they'll respond by saying that users choose to download and run Brave. But the long term financial success of the project is dependent on most users either not knowing or not caring that their browser is inserting ads into webpages and taking funding from publishers (and maybe "opt-in" to seeing replacements ads through some UI dark patterns, I don't know). Frankly I don't see any real difference between this and the average toolbar that promises to "add value" to the browser.
Brave has the worst business practices of any open source company I know of, and they're a blight on the community in general.