How far are you with the joomla development tutorials.
Everything is possible...
What I would do -> create a new form field (jomsocial_friends) & render it in the form. Now I'm not really sure what to do with the db. Maybe the best thing would be to have a column for this field -> this way one can directly select the hotspots that one needs for the user. Another way would be to store the value in the params field, but then you'll need to grab all the hotspots and go over the params field which will be slow. So, most probably best will be to add a new field. Or is the public, friend & private status related to the joomla ACL in any way? If that was the case one could use the asset_id...
Once you have all this comes the funny part. You'll need to modify the queries. You'll need to modify the query that loads the hotspots (most probably in the hotspots model) & you'll also need to modify the tiles model.
Then you'll also need to modify the layout and add a button for the preferred privacy -> modify the js so that it knows what to do with the privacy and send correct requests to the server.
At the end - a lot of work
Regards,
Daniel