At this point we just have to sit back and see what happens on Market East. It's architectural stock that today would generate restored building projects perhaps was decimated in the late 70s and early 80s. It has hulking buildings like the Gallery that lend themselves to discount retailers just as much high end anchors. New development will be large scale (Disney hole, Snellenburg site) and anything can happen.
A trip to PhillyHistory reminds us that for much of the 20th Century, Market East was nice in places, down at the heels in others, and (I say this wistfully) covered in mid-century garish neon signage.
It has, as many previous posters said, long been a street everyone uses; it's never had a niche market. We can expect it to look better via redevelopment in coming years, but it will perhaps always be a diverse setting of races, incomes, and businesses appealing to many groups. What better environment to be named for market houses, which have always served such a role.