Escargot already supports MSNP14, along with MSNP15, but it has limited support for MSNP18 and MSNP21 on the public server, so WLM 2011/2012 wouldn’t work with Escargot anyway.
As for the proxy idea, that’d just send the protocol data to the proxy server in its own protocol, which will then send it to the target server in its protocol. Basically, it’s as if the Messenger server had another layer that just transmitted the data it received to the server it relays. Considering Escargot’s lack of sufficient MSNP21 support, that won’t work either. Also, sniffing the data the program sends won’t magically make it work. Specifically what part of monitoring the connection will make WLM 2012 work?