I've done some triage to figure out if there are additional items that warrant discussion. Building on #16 and what did not get addressed in yesterday's meeting, that gives:

4. Interaction of cross-site cookies and SameSite=None.
5. Adding more contextual information to requests: Sec-Fetch-Ancestors? w3c/webappsec-fetch-metadata#56 & Fetch-Metadata to indicate when the browser is in a partitioned context w3c/webappsec-fetch-metadata#80 (see User agents should indicate to servers whether a request is cross-site CHIPS#2 for context).
6. Ephemeral partitioned third-party storage (including cookies) by Brave: Top-Frame lifetime, partitioned storage for embedded frames proposals#18.

(Obviously open for further additions, but I figured I'd file this directly to keep track of it.)

Edit: I moved what is now 6 to the end as it's somewhat unrelated to cookies.