Yes, but it's STUN that sucks. If the software ships with a public (on the internet) relay/STUN server for connecting the two clients, it won't work if either aren't connected to the internet, even though the clients could still be on the same network and reach each other.
/? STUN: https://hn.algolia.com/?dateRange=all&page=0&prefix=false&qu...
There is a Native Sockets spec draft that only Chrome implements;
"Direct Sockets API": https://developer.chrome.com/docs/iwa/direct-sockets :
> The Direct Sockets API addresses this limitation by enabling Isolated Web Apps (IWAs) to establish direct TCP and UDP connections without a relay server. With IWAs, thanks to additional security measures—such as strict Content Security Policy (CSP) and cross-origin isolation— this API can be safely exposed.
Though there's UPNP XML, it lacks auth for port forwarding permissions. There's also IPV6.
Similar: "Breaking the QR Limit: The Discovery of a Serverless WebRTC Protocol – Magarcia" https://news.ycombinator.com/item?id=46829296 re: Quick Share, Wi-Fi Direct, Wi-Fi Aware, BLE Beacons, BSSIDs and the Geolocation API
That seems like a nonissue for the purposes of this discussion though, in terms of user uptake. Tiktok and Facebook and other websites aren't exactly focused on serving to people on the same network.