There is really only one existing WordPress integration for Facebook Instant Articles. It is from Jack Spurlock, a developer at WIRED. Facebook has a limited spec for supporting Instant Articles, which at a base level can just use RSS, but deeper integrations would require access to the program for further testing.
Automattic is working on a plugin to support Facebook Instant Articles, and some WordPress.com VIP customers seem to be using it in production already. I discussed the plugin with a member of the VIP team, and I understand it should be ready for testing and implementation “well before” the April 12th date Facebook has given for open access to the program.
Instant Articles require hosting the content on Facebook itself, and that means subjecting your content to Facebook's advertising, and therefore not your own. I don't know any details about how they'll be managing ad revenue sharing with publishers, if at all, but I imagine if they do share revenue, it'll cause a big uptick in support for the feature.
For their existing Instant Articles partners (which are all big publications), ad revenue is negotiated, I think, on a per-publisher basis. I'm personally partial to AMP, Google's more open approach, which Automattic also has a plugin for, but Instant Article support may become a necessary evil for folks that want to take Facebook seriously.