> hex / base64 / json / xml
Literally everyone. Go is not exactly a stand-out XML handler either.
> TLS (1.3) / x509 / aes-gcm / sha-2/sha-3 / X25519 / ECDSA / ed25519 / crypto.rand
The prevailing idea even within the Go community today is that probably too much of that is exposed and instead the stdlib should be focusing on higher-level primitives.
> http / html templates / json-rpc
Go's HTTP stack is very good. Most languages do have a worse one, though.
The templating language is interesting, I'm glad it's there, but I think there will be widespread dissatisfaction among developers coming from other languages within in the next few years and you'll see it languish in favor of a 3rd party library. I would not choose a language based on its stdlib templates (and if I did I'd choose Perl).
I bet they will come to regret jsonrpc in stdlib.
> big integer math, zip
Table stakes.