Thanks for explaining some misgivings on State St Media street running high level platforms. But since you're not the poster who first mentioned it, I expect to read other reasons when MichaelBug replies
Alas, I can't agree that State St's Media's main business drag. The automobile rules, and I believe that has made Baltimore Pike, 1 block away, get more businesses than State St.
I agree that it's probably not politically palatable further to restrict automobiles. Although they didn't do it long term, or often, or recently, Media had once in a while closed State St to automobile traffic for weeks at a time some summers, and promoted the 'trolley mall'. The last time I remember them doing it the centerpiece, at least in my mind, was free shuttle rides on a 1920's vintage 'center door' trolley. They haven't been on the property since the early 1980's, and I don't know for sure that Media's repeated any long running automobile bans.
Are you sure you can call State St one of the most important segments? It's the end of the line, frequently gets bustituted for snowfall, and doesn't seem to me to have many passengers.
The 102 Sharon Hill line's street running I'd count as one of the important segments. It's a couple of miles from the end of the line, so SEPTA would have to cut the line back a lot in order to eliminate that stretch. But it's double track on a wide street.
In myrtone's defense I believe he lives in Australia, so might not know as much about local terms as Philuffians like you and me.