[gettodachoppa]

I like Brave and trust Brendan Eich, but what happens when they cash out and the next owners decide to monetize all this data?

The current policies don't allow it, sure. But then there will be gradual changes to those policies, and all sorts of dark patterns that make 99% of users leak their data (think "enabled by default but opt-out").

Is there any guarantee against this?

[BrendanEich]

We don't collect any data, so there's nothing to "monetize". We bring ad matching and blind confirmations to the browser, no need for collection.

You have to realize data is worth less over time -- a lot less. So the issue would be whether users stick if (heaven forbid) a change of control left Brave in the hands of unethical owners. By design, open source, network sniffing, and other auditors would catch wise and flame such a corrupt Brave into the ground. That's the best we can do here. There is no safety property ("X" holds for all future program states) enforceable on a company.