"Would the decision to open such a new store, at that specific location, be indicative of a significant market of model railroaders in that area?"
I don't believe that was the rationale. It's a mall that sees 17 million people a year visiting. This is an experiment in opening a combined store/layout display to encourage people to consider the hobby and see what is possible. Suspect there will be more than one layout, and focused at least in part on children. Should be interesting to see what they've come up with in terms of displays/operating features for those who wander in.
