If you encode each packet in a QUIC stream with it's own stream ID, and close QUIC streams after a timeout, you can use QUIC for unreliable unordered transports as well.
Good idea, THANKS A LOT! It has crossed my mind too, but I've discarded without giving it enough thought. The reason why it MIGHT work, is because of the implicit stream creation in QUIC (no handshake, nothing, just single UDP packet). There will still be some overhead, but probably it won't be "too bad".