The shopping portal, reviews, AWS, Kindle, and Echo are all direct touchpoints with users of some sort.

If you're going to launch social, you could do a lot worse for a starting point...

And in a broader sense, I'm much more optimistic about building a social network to unify disparate features that people already love, vs imposing one from the top down (e.g. G+). FB only got away with the latter because of being first, and seems to be pivoting to backfill as much functionality around it as quickly as possible.

This would possibly be a first step for AWS to start moving up the stack.

What does that mean?

It means Amazon renting you access to business software rather than access to computers on which you can run your own business software.