It is a big idea and would work if the people are there, once its less populated like any online community it dies slowly and surely. For sony this could be big, granted the internet, sony computers, PS3, and later playstation generations. Perhaps this could grow and not plummet.
I would say this is a good step and does need the broadest approach as possible maybe include the PSP, or another affiliates entangle another sort of IM service with it.