This is tremendously helpful, thanks! I'll start up an MVP sub-page, too :)
I've been mulling over the interwiki stuff, and I realized that one of the big benefits of not working on the Feed view in the first release is that we don't necessarily have to worry about all the thorny "what happens when this board is semi-protected on project x and I'm an admin on project y but haven't been autoconfirmed on project x?" issues yet – focusing on individual boards means we're sticking closer to the current talk page mental model, which is very much per-project based. Deploying to a WikiProject discussion space (or the Flow portal talk pages...) will give us an opportunity to see if and how we want to aggregate topics from multiple boards and display them to the user, but it's not a hard first release requirement.
Also, I seem to have inherited a bounty of ee-related mailing lists – do people care which one we use to share work like this? I figured the e2 list (E2 development team) might be better, as this list (Editor Engagement) has a broad WMF and non-WMF audience and seems more appropriate for general idea-sharing, rather than announcements aimed at specific teams of staffers. I don't care as long as we're consistent; I'm just worried that if Flow announcements start to dominate here, volunteers and non-EE staffers will feel less comfortable posting non-Flow related things.