However, he also said that even though retailers have made plans, their models will probably evolve over the years as they see how consumers react to the changes. “A lot of it is educated guesses.” Most retailers will have to reformat store space, since with a significant amount of product going directly to consumers who order online, they now have 10% to 30% more space than they need.

But new industrial distribution and fulfillment centers will be critical. “An estimated 30% of US industrial big-box demand has a correlation to e-commerce,” according to the report, “and this will not abate anytime soon. Major retailers continue to open new fulfillment centers that offer access to the nation's key population centers and infrastructure, and are opening smaller centers to enhance coverage in secondary markets.”

And to ensure maximum flexibility, many retailers will partition their new warehouses to handle several different operations. JLL points to Carters.com, for example, which now occupies a 1-million-square-foot facility in Braselton, GA. The company divided it into thirds to simultaneously handle wholesale operations, which ships goods to a big-box retailer, inventory replenishment, which ships to brand name stores, and fulfillment operations.

Many companies, however, won't have the funds to build the new-style facilities pioneered by Amazon.com and others that have 40' clear ceilings, and employ triple the number of people traditionally used. Others will refurbish existing facilities to give them greater flexibility, and for some 3PL firms will start to play a bigger role in their business.

Whichever way retailers choose to go in the next few years, the changes are here to stay. Currently, “59% of the country's population shops online; millennials, a generation raised on technology, comprise the majority,” JLL researchers say. “By 2020, they will account for 30% of retail sales.”