> will it be possible with project moodlenet that student SA of university A could enrol at the course B1 of university B?
No, Martin, this is out of scope for the moment. University logins/enrolments/authentication/payment is a very idiosyncratic and sensitive thing that we won't be tackling now. What you are talking about is addressed by MNet, and needs to be very explicitly set up between particular Moodle sites.
That said, I do hope the MoodleNet account/identity will become something you use to log into all sorts of education-related sites via Oauth, much like you can you use your Google/Facebook/Twitter account to log into many sites today.
> the community hub functionality will also be cancelled soon or within the next years?
MoodleNet is designed to replace that, yes. Including (most importantly) the sharing and curation of entire Moodle courses as well as individual Moodle activities in Moodle backup format.