I wonder how much different it is from Wireguard + netcat. Both run encrypted channels over UDP, but somehow differently. What does QUIC offer that Wireguard does not?
Wireguard doesn't, which is why tailscale took off so much, since it offers basically that at its core (with a bunch of auxiliary features on top).
Show me some wireguard discovery/relay servers if I'm wrong.
Also, QUIC is more language-agnostic. The canonical user-space implementation of wireguard is in Go, which can't really do C FFI bindings, and the abstractions are about dealing with "wireguard devices", not "a single dump pipe", so wireguards userspace library also makes it surprisingly difficult to implement this simple thing without also bringing a ton of baggage (like tun devices, gateways, ip address management, etc) along for the ride.
If you already have a robust wireguard setup, then of course you don't need this and can just use socat or whatever.
QUIC is a transport protocol that provides a stream abstraction (like TCP), with some improvements over TCP (like built-in support for multiplexing streams on the same connection, without head-of-line blocking issues).
Wireguard provides a network interface abstraction that acts as NIC. You can run TCP on top of a wireguard NIC (or QUIC for that matter).
QUIC is all UDP, handling the encryption, resending lost packets, and reordering packets if they arrive out of order. The whole point of QUIC is to make it so you can get files transferred quickly.
WireGuard doesn't know the data you're sending, and netcat+TCP is stuck with the limitations of every packet needing to be sent and acknowledged sequentially.
In fact, it's one of the main reasons I use Wireguard. I can transition between mobile network and wifi without any of the applications noticing.