I'm a little unclear on the subject of opportunistic encryption of the HTTP:// address scheme in HTTP/2.
According to the bug report, it looks like it's kinda optional, and an afterthought:
There's also a FAQ entry:
Does HTTP/2 require encryption?
No. After extensive discussion, the Working Group did not have consensus to require the use of encryption (e.g., TLS) for the new protocol.
However, some implementations have stated that they will only support HTTP/2 when it is used over an encrypted connection.
However, it's unclear how it relates to opportunistic encryption, where implementation would be [kinda] mandatory, but actual support [somewhat] optional.
However, according to IETF "Pervasive Monitoring Is an Attack", Best Current Practice 188, it would seem like opportunistic encryption is supposed to be made mandatory is all protocol designs:
Is HTTP/2 being designed in violation of BCP 188, RFC 7258?