It is, but that doesn't change the fact that I'm still more curious on that front. The wiki page has a few sample servers [0], but again, those don't meet your criterion of popular.
I realize that the initial RTT reduction isn't so relevant in the context of large dependency graphs, but especially in the context of packet loss, the proper multiplexing across flows seems useful.
There are also a number of other QUIC-based features that might be relevant, since it does essentially reimplement the relevant parts of the TCP stack, so parameter choices might be better suited to today's internet (as opposed to 1980's).
[0] https://en.wikipedia.org/wiki/QUIC#Server_support