I think there are a few reasons it will be hard to switch to this model.

It's the same model advertisers use though. Here's the flow for ads:

1. Ads load from the advertiser, with metadata about which website to pay
2. Periodically, advertisers pay the website for showing ads

All that's changing is the browser vendor is paying instead of the advertiser. So I guess think of Mozilla "paying" for ads, but not showing anything, and Mozilla's non-ads would show if a given header is present.

Another is that sites want to be able to charge more for popular content. That’s easy with advertising

Sure, and users could decide to see the ads or pay the premium to avoid them.

And yeah, I agree that most sites overvalue their content. This makes that more transparent, so users will gravitate toward the better value. I personally avoid a lot of high quality content because viewing it is too much of a hassel, a privacy violation, or too expensive (I'm not getting another subscription to read a handful of articles).

I don’t think Mozilla is interested in this sort of solution.

Agreed. But unfortunately, Mozilla seems like the best chance we have here. Brave replaces website ads (big no-no for many sites), Chrome doesn't EB want ad blocking at all, and Microsoft is cooking its own ad network.

So the most obvious niche left is an un-ad network, where you can pay to not see ads. Yet Mozilla wants to make "ethical ads" or whatever, which doesn't really solve the problem for people who hate ads.