I'm unsure what you mean; intermediaries can absolutely cache responses regardless of whether they are retrieved with HTTP or HTTPS. One great example of this i

I'm unsure what you mean; intermediaries can absolutely cache responses regardless of whether they are retrieved with HTTP or HTTPS. One great example of this is Cloudflare itself, acting as a CDN for backing systems which serve content to Cloudflare protected with HTTPS. If you are talking about a separate, non-intermediary cache service, this is neither part of HTTPS or HTTP. While there are certainly third party implementations that work this way, there isn't a generalized approach out there to solve this. Instead you have things like software caching services specific to a particular vendor, or things like Google AMP.