CERNET/CERNET2 started from stateless translation, and is a fixed network. So I would be careful saying "never". But frankly, the solution for the fixed operators is not translation 6<->4; it is IPv6 deployment.
I have to agree with Fred here. While there may be advantages to
PT in some cases, native IPv6 deployment has the advantage of
preserving end-to-end (choose your definition of e2e), among others.