Totally agree that a DNS based replacement to the suffix list would make sense. Especially with more secure forms of DNS like DoH or Dnssec.

That said I don't know about making cookies shareable across TLDs. That seems like allowing more privacy nightmares; at least today if you want to share you need complicated redirect dances that make you question if the user perf hit is worth it. I think there was some proposal for a mechanism for allowing non partitioned 3rd party cookies which seemed more sane to me, forget what the details were and if it ever made it beyond just a proposal.

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