Traffic steganography: The techniques used are just recognizable and an algorithm to train. Especially if you also have the source. Domain Fronting: Nice, but if it is so common, you can just ban the CDN providers (or oblige them to operate within China according to their rules) and Amazon & co are really not happy with it, so they will work against it themselves.  Moreover, there is a payment structure (other than with eg Tor), which makes it possible to follow users via the payments. Of course, there are methods for circumventing that, but it is an extra step.
I would not be surprised if the Chinese government would eventually just block everything that is not HTTP / HTTPS, and just apply MITM to HTTPS (break open encryption and self-signen with a root CA that you will have to install), and block everything that they can not read yet. The technique is there, at work they do exactly the same, the firewall reads everything.