What I suspect will happen is that the major proxies (e.g. WebSense) will block plus.google.com just like they block mail.google.com now. No reason to block all

What I suspect will happen is that the major proxies (e.g. WebSense) will block plus.google.com just like they block mail.google.com now. No reason to block all of google - likely, they just haven't gotten around to it yet.