Here on chrome devtools we are planning on a bit of changes involving network/resources, timing and import/export. We are heavily interested in a newer HAR spec that would support much of the new technologies available. I'd be personally happy to help develop a new spec with you and use this new spec as our basis for import/export for analysis.
As for describing HTTP2 info, here is some info worth discussing:
* Push Promise information (including timing)
* Resource priority and priority changes
* Define how upgrade requests from HTTP1.1 to h2 are surfaced
* Field for streamID
* Ping packets
* HTTP2 connection settings
* Frame details (like size of frame, ack, and timings)
Some other things worth discussing:
* Initiator data
* Packet loss
* Some kind of histogram of speed data was received/sent
* Although Quic is not common yet, it introduces the ability to send multiple copies of the same packet.
Obviously many of these will not be defined in this spec, but they are worth discussing.