I've been thinking about some possible implications of the East Market design, and Something I hope a developer takes advantage of is the continuation of the pedestrian alley retail corridors like the forthcoming "Chestnut Walk."
It would be quite easy to design a completmentary corridor through the "disney hole" at 8th & Market, and these could be bookends that set the president for a Gallery remodel in that style. Although its unlikly PREIT would completley open up the entire mall concourse to the sky (requiring several floors being removed in areas), it could redesign the enterances from the sidewalks to be more fluid, and feel more like an indoor/outdoor space. This would be most easily done at 8th/Market where the steps go down to the Gallery, by building a high (glass?) over-hang ceiling with no walls or doors, just modern artistic support pillards, and making the transition from street level to gallery level more gradual, while mostly uncovered. (Ideally I would like to see the whole thing razed and make an extra large sidewalk on Market St as the primary pedestrian corridor, but this is less likely in the near-term)
The other main component I hope Jefferson University/SEPTA/Philly/PREIT build is a public squre with a new Jefferson Station Enterance facing it. Something that is modern and bright to match the Market East design, and with a clear main enterance to the Station. This would mean buying and tearing down Burlington Coat Factory, but that could easily be relocated elsewhere (maybe at 8th/Chestnut in this layout?)
Anyway... have a look, let me know what you think.