The fact that this city never built the balance of its planned subway system is today a sword of Damocles for those of us who would like to see it expanded.
Had they fleshed the system out as they were originally trying to, there would today be subways along Ridge, Germantown, and the Boulevard. But Ridge and Germantown run through both extremely wealthy districts, e.g., Manayunk, Chestnut Hill, of the city, as well as extremely poor ones, e.g., Strawberry Mansion, Nicetown, and Northeasterners have been most resistant to the Boulevard subway expansion, although the original plan when the Boulevard was created was to put a subway line there too, as yet another spine.
The main current service expansion proposals in Philly right now are two PATCO expansion, one into South Jersey, the other a light rail line along the waterfront, as well as a route restoration along the R3 from Elwyn to Wawa (it originally went to West Chester, so even then...)
There are a number of threads on Philly Blog and Philadelphia Speaks that talk about this issue:
http://www.philadelphiaspeaks.com/fo...alignment.html
http://www.philadelphiaspeaks.com/fo...n-pa-side.html
http://www.philadelphiaspeaks.com/fo...ents-plan.html
http://www.phillyblog.com/philly/showthread.php?t=70890
http://www.phillyblog.com/philly/showthread.php?t=65900
http://www.phillyblog.com/philly/showthread.php?t=66229
http://www.phillyblog.com/philly/showthread.php?t=70376
...and many more. The point being, we all have our own ideas about what to do about our lack of rail mass transit.