In light of the roadmap and the work you're doing, should Requests for comment/Page metadata be closed as an issue that's been decided, or are there still some metadata topics we should invite the community to discuss?
Topic on User talk:GWicke/Flow
As a first step, we intend to separate page properties from content in HTML DOM. This requires little discussion with the wider community, as users don't normally interact with HTML directly. For wikitext users, nothing will change for now.
Removing page properties from the wikitext however will definitely require discussions. In templates, I expect them to stay as long as wikitext does. In the page itself we'll still need very good UIs for diffing and editing of these properties. We plan to work on diffing, and a page property edit UI is being developed as part of the VisualEditor. Right now this is still fairly far out though, so it is difficult to discuss specifics.
I think it makes most sense to just do the work that can make this an option. Once at least prototypes of the user experience are available we should be able to discuss specific options without too much hand waving.