My personal opinion (which might be wrong!) is that jonnath is trying to reassure people that 'Directory Tiles' is not about slapping random ads on the newtab page, and is not going to just ride the trains to release. They're going to stew in the Nightly channel for a while while we iterate on them and figure out how to make them useful to users.
What I don't see is an assertion that the final feature won't involve some form of revenue. There's been no final declaration, but my understanding was that the suggested system involved choosing sites that are useful to our users, and then going to those sites and discussing payment for the placement, rather than letting sites come and pay us to be put on the page. This is very similar to what we do with the search box: we choose Google as the default because we think they're the best default for the users, not because they got to us first or paid us the most[1].
If you want more details about the implementation that's going to land on Nightly, check out the tracker bug for the feature and the dependent bugs: https://bugzilla.mozilla.org/show_bug.cgi?id=973273
(And remember kids, Bugzilla is for input on the implementation, discussion about the feature itself goes on a mailing list like firefox-dev[2]).
[1]: Granted, if we choose Google and Google said "Hah, no money for you" then we'd probably go to another provider because we have employees to pay, but this becomes a more important distinction if, say, Bing wanted to pay us more than Google.
[2]: https://mail.mozilla.org/listinfo/firefox-dev
Disclaimer: I'm a webdev for Mozilla, and can't speak for the people actually working on Directory Tiles, only as someone who knows how to navigate Mozilla's public information.