As discussed recently, there are various properties of the SameSite cookie attribute that need to be evaluated for how they would work in a partitioned world without third party cookies. A probably incomplete list of things I've seen mentioned:

1. A1 -> B -> A2 nested documents and cookies (and SameSite=None) #31
2. Do we still allow cross-site POST with SameSite=None?
3. When an embedded iframe navigates from a cross-site context to same-site, SameSite=None cookies are sent. Do we want to keep this behavior?
4. Sending cookies as part of FedCM requests (What cookies are passed in the Sign In API call? fedidcg/FedCM#248)

Underlying is the question of what the SameSite attribute itself should look like in the future. We could, for example, decide to deprecate the attribute entirely and use alternative attributes to preserve aforementioned security-related use cases with more granular control.