How is this different from a VPN over UDP, like OpenVPN or Cisco Anyconnect?
These kind of tunnels allows custom, obfuscated protocols.
It's used to bypass DPI where known VPN softwares are already filtered.
My experience is, that UDP is also blocked like TCP. The only possible work around is then IP over DNS, which works but with very very limited bandwidth.
What about tunnel over HTTP? That can be much better obfuscated. Tunnel over DNS can be easily filtered out by just checking for the traffic amount (for example to block VoIP the ISP should just degrade DNS if traffic amount is above a treshold for a user)