Not every network is as simple as a router in front of a laptop. And some may treat websocket traffic differently. And do weird DNS stuff. Every time your basic assumptions are wrong, your client loses a user, and you don't even have a way to detect that.
All these signals will either be too weak and let through enough false negatives as to be essentially useless, or too strict and produce so many false positives that a significant portion of the legitimate users leave in frustration. Unless you are some oppressive regime cracking down on VPN usage, I truly don't see where this will be useful. I guess it's helpful to compile the list of modern methods for detection and fingerprinting, so VPN providers can mitigate them.