We’re evaluating it in the broader context of the opam security requirements; you can read the last meeting notes about this topic from last week.
The good news is that when sharing binaries is not involved (such as with a CI caching workflow as you are using), it is considerably easier to engage binary caching. I expect this to be the first usecase, but we do need more people to try out the opam-bin prototype. Feedback such as yours is very valuable, thank you!