Hi, (here goes a disclaimer about me posting this email as volunteer tech ambassador in Catalan Wikipedia in my personal time)
While Flow might not be ready to make happy core enwiki contributors, in my humble (and again, personal) opinion it is clearly ready to make life easier to dozens (hundreds?) of Wikimedia projects (the smaller, probably the merrier). The Catalan Wikipedia project has gone through several iterations of Flow adoption, they basically want more, and they basically will get more. Their goal is simple: Flow everywhere.
This is not an exaggeration. The communities that work actively and directly on bringing new editors (with workshops, editathons, collaboration with schools and other face to face interactions) know that VisualEditor is a key tool. Once new editors have been trained with VisualEditor, there is no way they will enjoy or even understand why they should learn wikitext-based conventions to discuss and collaborate. Flow is the natural VisualEditor companion, and new users don't even "love it", because for them is just natural.
I'm happy to see that the possibility for users to opt-in to convert their user talk pages to Flow is close to deployment. It is an interesting way to let users show their interest and preference. I hope projects willing to enable Flow in more places will get the tools or processes to do so. I understand the demands of big projects with complex processes in their discussion pages. I just hope those requirements don't become an obstacle for the many more smaller projects that can benefit today from Flow. Time will tell.
About Flow for third party MediaWikis (let me change my hat again, now as admin of a small wiki in a 3rd party wiki farm), at least https://miraheze.org/ is offering Flow to wikis requesting it. It works, with script to archive wikitext discussion pages an all. If they have done it, I guess other third parties can do it.
Anyway, did I say Thank You Flow Team? :) You rock, and you will continue to rock.