I too am a little torn. Procede to reopen the corridor to transportation of some kind, or hold out for a perfect scenario which likely isn't going to happen.
If they didn't remove the rails, they'd have to engineer a way to keep them from poking up after a heavy storm and creating a hazard on a bike trail. Nobody wants to make a trail only to have a recurring hazzard pop up over and over. And I'm pretty sure nobody wants to permanently pave it as a busway.
Is it really that far-fetched to turn it into a high quality bike corridor, that connects to the West Trenton line somewhat near the middle? Put a few bike racks near the Bethayres station, grade the corridor and patch up the bridges, repave a few of the lots on the Newtown line, allow free parking during day and see what happens? If it adds a few SEPTA riders, great. If not, then hopefully somebody is getting some exercise. I'd bet with a few signs along the corridor suggesting it as a version of a park-and-ride, it could actually get a few regular users. Plus with the light weight of bikers, the existing bridges would probably be pretty easy to reinforce. Like everyone else here, I'd prefer it being a rail corridor, but I don't see a benefit to just letting the corridor further rot away for another 20+ years..
PS. I work in the boonies of Mont.Co, and I see people biking to work all over the place, including here in most kinds of weather. While my knees wouldn't cooperate on such a venture, the riders I know just shower and change their clothes at work. (I'm betting lots of places downtown would have better facilities than this one as well)
Just my two cents, feel free to disagree as usual.