No-one else has posted in this thread yet, so I may as well share a discovery I made the other day. After substantial amounts of trawling, I found what appears to be the official (?) Chinese Messenger client. Here's the website:
http://www.windowslive.cn/Get/
There are three different versions of Messenger there, 7.0 for "Windows 2000 users," 2009 (14.0.8117.416, the final build of that version), and 2011 (15.4.3555.308).
I downloaded the 2009 one and its only obvious differences are the weird installer (it's a little uglier and behaves a bit different to the normal one) and that most everything is displayed in Chinese. However, another curious thing is that normally, if you try launching and signing in to Messenger 2009 out of the box, it'd decline you and say had to download the latest version of Messenger to continue. To circumvent this, you could either run the program in compatibility mode for Vista SP2 or lower, or you could modify the registry string and change it to the latest version. But with this "Chinese" client, it signs you in with no update prompts of any kind.
I wonder if this particular version of Messenger connects to the Chinese servers, or if it provides any use in prolonging Messenger's lifespan for those who wish to continue using it after April 8?
Someone please contribute to this discussion and give their input.