Why not just conduct such discussion on the open list? That is the apparent parallel - the catch-all between and across projects list. Projects is a direct to project leads and nominated individuals list. It is used (deliberately) infrequently, and is the normal channel for (for example) commercial tenders that the foundation receives from time to time that may be of interest to projects and their communities. I wouldn't want to lose the ability to handle that, frankly, without posting to a public forum, and I don't see the point in further list proliferation.
Rather more important is the promotion of lists like open, which currently have few members and should have broader provenance and membership.
Best
Ian
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Sent from a mobile device. Apologies for typos and/or brevity.