http://i3xi5qxvbrngh3g6o7czwjfxwjzigook7zxzjmgwg5b7xnjcn5hzciad.onion/proposals/348-udp-app-support.html
In fact, Tor's many exit nodes already share similarity with some types of carrier-grade NAT.
Applications will need to assume very little about the IP address their outbound UDP originates on, and we can use that to our advantage in implementing UDP for Tor. This body of work is invaluable for understanding the scope of the problem and for defining common terminology.