The BRA guy makes an excellent point. With just these two projects, that's 2.25 million sq ft. of space.
Size of the Cambridgeside Galleria: 900,000 sq. ft.
Size of the North Shore Mall: 1.7 million sq ft.
Size of the largest Wal-Mart in Massachusetts: 210,000 sq ft. (Its in Leicester)
A Nordstrom or a Bloomingdale's is probably not going to want more than 200,000 square feet. So if you are fortunate enough to get both, that leaves 1.8 million sq ft of space (gross) to still lease. Failing to get those two and/or a JC Penny, you are left with big box stores as your only other option. I don't think conventioneers are going to throng a Target, a BestBuy, or a Bed, Bath, & Beyond.
As a point of comparison, there is a big retail complex just across the river from Washington known as Pentagon City & Pentagon Row. (Its named after the adjacent 6.5 million sq ft (gross) building.) The anchor stores are Macy's and Nordstrom. The square footage of Pentagon City & Pentagon Row is 2 million square feet, and there is another 400,000 square feet or retail nearby. Besides having a subway station (with different lines) this retail area is surrounded by 14 million sq ft of non-government-owned office space, 10,500+ housing units, and 5,500 hotel rooms. There is, however, no convention center.
http://www.arlingtonvirginiausa.com/index.cfm/6223
And yes, its pre-cast city .