There is absolutely nothing visionary about it except that its a really nice cash cow.
I don't expect it to last through 2015. 2017 is way to long
I would invest for sure if there was such a thing as Facebook X labs.
But nope lets go with timeline
The land-line has been effectively killed off (the last X million accounts will be slow to go, much like the last X million AOL accounts have been). Facebook would be the land-line approach, social networking voice telephony in general.
Vastly more people now get their email through a web browser - "webmail" - than via dedicated desktop email software (eg Outlook). Facebook is Outlook, social networks are email in general.
I'm not saying Facebook will die like that of course, rather your comparison is all wrong.