HTTP2 doesn't require encryption but it does compress the headers. I'm guessing compression makes it too CPU-intensive for telecoms to manipulate the headers on the fly.
This is in progress. HTTP 2.0 does exactly what you specify. The tcpinc working group at the IETF is also looking at adding this at a lower level for all TCP connections.
It's unlikely they'll ever get mass usage because both are uncomfortable to work with.
If a certificate is compromised, changing it means all pinned clients will get a huge warning. Either the user ignores the warning (in which case pinning is useless) or he doesn't and the site is harmed. Keeping a compromised certificate is even worse.
For WoT you first need a web of trusted individuals.
Unfortunately key distribution over insecure channels is still an unsolved problem.
