Thanks.
Seems QUIC is preferred over uTP, which is fine. It's a UDP-based protocol and in principle all the hole-punching and other NAT traversal methods should be supported.
Unfortunately, seems QUIC is "experimental" and doesn't seem to support NAT traversal (automatic gateway discovery is only available on the "dev" branch, for example).
NAT traversal seems like a basic requirement for a P2P decentralized protocol.