I think the idea of a plus messenger would be cool, although time-consuming, expensive and pointless(we have msn, why do we need plus messnger).
However, i would download a plus messenger if it could connect to msn and have it's own plus network. For example plus features disabled on it's msn(because anyone with plus would have the messenger).
P2P wouldn't be a bad idea. But
IF he makes his own network what would stop that from going down? A dedicated support team?
It's very difficult to decide. I won't force him to do it, but if he makes one, i'll be like
!WAHEY!