My understanding is http/2 is out of scope. The purpose is to have functional http to implement the package manager. I would expect a high performance http client/server to be a third party library, not std lib.
In practice, it's very much an appropriate use case for multiplexing, if you ask me. But not having it isn't a dealbreaker either, IMO. It's a bit more work to support HTTP/2 and can be done rather transparently later on anyway, since the underlying transport can be switched and has an upgrade path.
Very much the opposite
[Edit] And it's quite feasible to decide later that http/2 was never needed for this usecase.