How does SPDY fit into this? Is QUIC to UDP what SPDY is to HTTP?
Almost: QUIC improvements are supposed to be put back in TCP, not in UDP. See the FAQ [0]
[0] https://docs.google.com/document/d/1lmL9EF6qKrk7gbazY8bIdvq3...
Slides here - https://docs.google.com/presentation/d/13LSNCCvBijabnn1S4-Bb...