I think this Lincoln Yards (bleghhh, that name) article from Curbed a few months ago provides a good idea of what the original conceptual massing was supposed to look like... And perhaps the render at the beginning of this thread still reflects some of that:
https://chicago.curbed.com/2017/7/26...-606-extension
(The master plan diagram within the link is very reminiscent of Studio Gang's other typical diagram illustrations..did they design this?)
Regardless, I think a lot of this is serendipitous for Sterling Bay since they created something that magically fits a big part of Amazon's needs...or maybe it's not serendipitous...