I suggest that I go and get temporary admin privileges on those wikis and move those pages out of the way and then create the appropriate pages. However, I'm not certain if I need to do anything special to set up the Village Pump pages in the current style.

That said, it may make more sense to engage the community (small though it is) and ask them if they'd prefer to do it?

Adding WMSE and WMFI

I agree it would be easier for everyone if we (WMF) could do this update, for them.
The only part I cannot do myself is "Move" those 2 current pages to be .../Flow subpages.

Once the current pages are moved out of the way, I (or you, or anyone) can copy the old "Description" from the Flow board, to the top of the [now empty] original location, plus add a link to the newly-archived Flow-subpage, plus add __NEWSECTIONLINK__ at the very top of the page.
That should be sufficient, and will re-enable those pages as discussion-pages that anyone with normal editing-rights can use.

For now I've requested move rights, once I've got those I'll execute on this. Did we want to use /Flow as the suffix, rather than /Archive?

Thanks! Re: page-names, I think it would be best to use the generic /Flow, for now. (Context: I already asked, in my last MassMessage to those 2 pages, if they wanted something different, but nobody replied. It's a minor detail, either way.)

I didn't see an option in the UI which would allow me to move the page, so I made the following API request:

https://fi.wikimedia.org/wiki/Toiminnot:ApiSandbox#action=move&format=json&from=Kahvihuone&to=Kahvihuone%2FFlow&reason=https%3A%2F%2Fphabricator.wikimedia.org%2FT401825%20-%20Moving%20read-only%20flow%20board%20out%20of%20the%20way%20so%20that%20users%20may%20use%20this%20page%20again&noredirect=1&token=redacted%2B%5C&formatversion=2

Just to decode that a little:

?action=move
&format=json
&from=Kahvihuone
&to=Kahvihuone/Flow
&reason=https%3A%2F%2Fphabricator.wikimedia.org%2FT401825 - Moving read-only flow board out of the way so that users may use this page again
&noredirect=1
&token=redacted%2B\\
&formatversion=2

And I got the following API response:

{
    "error": {
        "code": "contentnotallowedhere",
        "info": "\"Structured Discussions board\" content is not allowed on page [[:Kahvihuone/Flow]] in slot \"main\"",
        "docref": "See https://fi.wikimedia.org/w/api.php for API usage. Subscribe to the mediawiki-api-announce mailing list at <https://lists.wikimedia.org/postorius/lists/mediawiki-api-announce.lists.wikimedia.org/> for notice of API deprecations and breaking changes."
    },
    "servedby": "mw-api-ext.eqiad.main-5c86596fb9-vlh4j"
}

I've double checked that I do have appropriate local admin and global global-flow-create permissions (until tomorrow…) so I'm a little surprised by this.

I'm not sure how best to go forward down this particular path, so I think my next move is to add a flag to the archive script which would enable it to move standalone flow pages and to re-run that once the change has landed.

See T382791

With some help from @Urbanecm_WMF, this is now done.