I'm not sure if the FTA provided money to the Girard Ave Light Rail project, I seem to recall the FTA pulling money from the project, eliminating the possibility of new LRVs and leading to the rebuilt PCCs for the line. However, if I remember incorrectly and there was FTA money used to build the line then the FTA is going to want to see their money used. Several capital improvements projects have changed after the FTA told the TA responsible for their operation that their plans were unacceptable. Amongst others I know the 63rd St Tunnel project up in NYC was supposed to carry the V Queens Blvd/6th Ave Local train, but the FTA determined that it's low TPH would not provide the requisite ridership for it's investment. As such the higher TPH, higher ridership F QB Express/6th Ave Local train was sent through the 63rd St tube, thereby fufilling the FTA's requirement.
It could be that SEPTA is finding itself in such a position, they may have an ultimatum from the FTA to begin operation by the end of 2004 or face penalties and such, regardless of where it's operated out of, and how much it costs SEPTA to do so. So long as LRVs are running on the 15 by Dec 31st 2004, they're in the clear. Given that SEPTA managers likely would just as soon have their desks clear going into December, and if there is indeed a pick in November, then that'd make the most sense to begin operation of the 15 with LRVs before the FTA comes calling.
Here's hoping that if SEPTA's forced to run the 15 out of Elmwood along with the 10 it improves their operations and finally sets up a system by which they stage operators out at loops to relieve operators heading off duty. It's ridiculous that SEPTA treats the LRV operations like bus operations, in that one operator is assigned to one LRV for their shift, and they have to put it back when they go off duty. Staging drivers out of Girard loop or Malvern loop would greatly improve their utilization of their LRV operations, since they'd no longer be deadheading all the time. Just send the LRVs out in the morning, have elmwood-based operators ride out to those two loops via either a crew van (likely much cheaper than a deadheaded LRV), or by taking a 36 trolley to a 10 trolley to reach their loop (you lose paid time, but save on vehicle maitenance, power, and such). This is likely a practice that the whole system could benefit from, there's no reason to constatantly run LRVs to and from Elmwood Depot throughout the day other than to meet demand for rush hour.