they already have a few (not neural-network though), that can classify encrypted data, such as described in the following paper...
And last month they they just integrated the techniques into their state-operated firewall, and then, bingo! it works! as a result many VPN services across the country are down (as reported in a NYT article linked below)
Perhaps a white list approach is being used now which would only allow those service providers that are willing to cooperate with the Chinese government to pass the filter...