Are you implying Let's Encrypt certificates should not be used for non-HTTP services?
Let's Encrypt's primary goal is to encrypt the web, and most of our decision making is based on that. It isn't so much about HTTP as it is the ecosystem.
You can use our certificates for any TLS Server use-case. I wouldn't suggest using our certificates for things which aren't TLS servers, though.
(The services are all TLS based. They are just not HTTP based, and CRLs are generally delivered via HTTP. And I'm not going to wrangle a HTTP client into my mail server, or worse, postgres instance. The latter could also work with a local CA, it's primarily SMTP that doesn't.)
(...or I just ignore revocation and cross my fingers it'll never come up...)
> Our new CRL URLs will be disclosed only in CCADB, so that the Apple and Mozilla root programs can consume them without exposing them to potentially large download traffic from the rest of the internet at large.
OCSP must-staple: free feature of TLS library, works
plain OCSP: hit & miss, depends on the client software using the TLS library correctly
CRL: no.
… that's the crux of this entire thread.