Good call! Honestly I just wanted to wrap it up before the holidays, but you’re right that a small section on Vary would have been useful.

Things like non-conforming caching services made me punt actual suggestions to a later article, as I wasn’t sure how my sense of the RFC interacted with the real world. HTTP Caching Tests seems like a great resource for this, but only includes Fastly out of the big providers, and it seems to be doing okay with Vary. https://cache-tests.fyi/