Also, wouldn't the premium of leasing or owning "retail" style property make the cost of maintaining the building too costly? I don't think Sears needs a datacenter on main street, or within a strip-mall.
After RTFA I pulled this:
"Farney acknowledges that many of Sears’ mall-based retail locations aren’t viable for data center usage. “I don’t think the industry is yet ready for a mall-based data center,” he said. “That may take some time. The stand-alone location is optimal.”"
It seems they are considering it more for certain stand-alone locations.
The real-estate deed for any mall location almost certainly precludes such uses by covenant. If they didn't, Sears would never have bought the property in the first place.
And it woudl be harder to secure you would find it hard to add a moat even adding a proper double fence might be hard in most of these store locations.
Data centers built by Google, Facebook, etc. seem to all be built from the ground up, and close to things like power plants.