> Unfortunately, there's no explanation of the mechanics of coordination and fault tolerance, so the hard part appears to be vaporware.

I think it's unfair to call it vaporware - Amazon doesn't tend to release vaporware. You can also be fairly confident this has been in private beta for some time, so we'll probably see a few blog posts about it from some of their privileged (big spending) clients - typically someone like Netflix or AirBnB. But I agree it would be nice to get some more information on the details.

As for the client library handling load-balancing, fault tolerance, etc - that might not be ideal, but as long as I don't have to do it myself then it might be okay.