Pop-up Stores Fill the Void

Pop-up stores have been coming on strong for the past decade. (Even longer if you count Christmas tree markets and other temporary stores that pop up seasonally.) During the current economic difficulties, with many vacant storefronts seeking tenants, pop-ups have become even more popular.
 

• Inc. recently reported on how to use pop-ups to (1) get the word out, (2) unload inventory, (3) test new markets, and (4) vet new retail ideas.
• The Wall Street Journal just did an article about pop-ups for (1) generating buzz, (2) testing new concepts (especially niche businesses), and (3) testing new markets. 
• The New York Times reports that pop-ups may be open for a few days or a few months, depending on the product and the marketing objective.
• The Denver Post reports that a pop-up store recently opened to serve as "an incubator of creative ideas" by featuring local artists.
• Target is one of the largest US retailers using pop-ups to build excitement about specific products, brands, and new markets. 

What will be the next pop-up trend to pop up?