Er, actually reading the specification, it's about proxying http resources, not https ones. This proposal is strictly better than the transparent proxying that's common on the internet today.
To distinguish between an HTTP2 connection meant to transport "https"
URIs resources and an HTTP2 connection meant to transport "http" URIs
resource, the draft proposes to
register a new value in the Application Layer Protocol negotiation
(ALPN) Protocol IDs registry specific to signal the usage of HTTP2
to transport "http" URIs resources: h2clr.
...
4.3. Secure Forward Proxy and https URIs
The Proxy intercepts the TLS ClientHello analyses the application
layer protocol negotiation extension field and if it contains "h2"
value it does not do anything and let the TLS handshake continue and
the TLS session be established between the User-Agent and the Server
(see Figure 8).
