• The Blueprint skin's sidebar on http://devhub.wmflabs.org has a blank space where a Discussion link should be (compare with the sidebar on http://livingstyleguide.wmflabs.org). I filed T103784.
• All the devhub Talk pages (sample) currently #REDIRECT the to the equivalent talk page on mw.org (sample), and invite the reader to discuss there. The mw.org talk pages are all Flow-enabled.

So, what should clicking the Discussion link do?

• Going to the local talk page and presenting a redirect is confusing to new users.
• I could enable Flow on the devhub labs instance. But it's very inconvenient for existing Mediawiki developers: they have to create a new username (there's no single-user login to labs), and they don't get Echo notifications of replies unless they revisit the prototype. Also, any discussions in Flow on the prototype site probably could not be migrated to the eventual location of the pages.
• I might be able to hack the Discussion link for each devhub page to link directly to the equivalent mw.org page.
• Perhaps "Discussion" in the sidebar could be hardcoded to link to a single Flow board on mediawiki.org, for all discussion, maybe https://www.mediawiki.org/wiki/API_talk:Data_and_developer_hub

I favor the last approach.
I have similar concerns about T103713: Enable Flow on LSG.