By terminating an udp stream and fetching the backend data using http 2.0?
This might be enough for static web and such, but in a "new web" you'd want to use all those nice features of http/3 which have no direct equivalent in http/2, like multiplexing udp streams for video and such.
And if you forward the udp stream itself, what do you do with the certificate? Use a selfsigned one with no expiration date and add a custom CA? Seems laborious.
nginx's implementation works. (but for me it caused a strange performance degradation with Seafile)