You can sign up for it here: http://landinghub.visualstudio.com/vsliveshare
It doesn't mention a date.
It only says 'may'.
It asks for an email "For a Microsoft enabled work or school, personal Microsoft, or GitHub account", which is not particularly clear.
The form and data goes to some 'hubspot.com', rather than to Microsoft. It is default-blocked by ghostery as a tracker.
The feature looks really interesting, the promo site and the experience of using it is, to use the technical term, poopy.
You can sign up for it here: http://landinghub.visualstudio.com/vsliveshare