Alright I'm a Septa employee. My boss tells me this:
As most of you know 59th Street and clearance is the main problem. 11 years ago when the 15 trolley became bustituted 59th was a one way street. Since then its become two ways with parking on both sides, causing the whole big clearnace problem. The residents of the area are staunchly opposed to making it one way again. Building a new switch to use tracks on 60th St is being considered at this time.
As for the 10 being bustituted, you must remember that the Calowhill pickings effective for Sunday have already happened, and there are a whole slew of Calowhill operators slated to work the 10. Instead of moving them all down to Elmwood for a short time, they would rather just have them run busses out of Calowhill.
Supposedly this whole 59th Street problem was only realized on Monday, leaving little time to rectify. How it slipped by that long is beyond me, considering K-Cars have been running around Calowhill testing the tracks and wires already.
I've heard the 10 and 15 should be back to trolleys in about a week, but don't hold me to that.