It also makes hardware offloads like TSO and LRO impossible, and increases cost-per-byte served by a factor of 4 or more. So if you have infinite CPU to throw at QUIC and/or low bandwidth or connection targets, its great. If you are concerned at all about server-side efficiency, its terrible.

FWIW, I work on the Netflix CDN, and specialize in server-side efficiency; we have had 100G flash CDN nodes for years serving at 90G+ in production. None of that would be possible with QUIC as it stands. I suspect our max B/W on these machines would drop from ~95Gb/s to 20Gb/s or less if we were to switch to QUIC.