@cwebber Back in the mid '90s I figured everyone would build their own "pull" caching infrastructure. But it always seemed as if the web was being intentionally built to sabotage any such effort. And now TLS makes it pretty much impossible.
Something like CoralCDN with self-certifying URLs and the ability/expectation for providers to PITM it might work. You'd need some way to get around the mixed content problem, though.