Patchou is an MVP (Most Valuable Professional). He does get into any beta he would like.
As far as Messenger Plus! not working properly with MSN Messenger this is expected. It was the same thing that happened with MSN Messenger 5.0. Plus! was unable to hook the internal workings of it causing that menu to be displayed. It is nothing new.
Once Windows Live Messenger 8 is released publically then Patchou will release a compatibility update to support it. Until then Patchou has bigger things to worry about.
Messenger Plus! source code is backed up on multiple sources but currently Patchou is trying to recover other data from it and wont be worrying about Windows Live Messenger 8 any time soon since it is still in beta stage (non beta testers shouldn't be using it) and not publically released.
We can actually close this thread and not worry about this any more.