I can actually see this happening. Sears locations might make pretty decent mini-DCs/Echo sales centers. Ironically, I feel like they could turn Sears into Borders and do OK. A mini DC center in the back- this could allow for 2 hour deliveries to more suburnban/rural locations. In the front they could have shelves of Kindle files printed out on paper. I know, it sounds like Ye Olde Book Store, but here an Echo thingy would replace the Dewey Decimal or human employee. Alexa would manifest as a racially and gender ambiguous animatron who would not only answer your questions but also serve free Kombucha when you pick up your prescriptions or sign up for a checking account (cash converts to Amazon credits).
I can see Amazon making them mini-malls within existing malls until the already struglling other stores can't exist anymore. Once Amazon has the entire mall- well that is when things get crazy!