SEPTA's got a lot of big infrastructure hurdles to clear before that can be possible. For one, the power system on the whole of the ex-Reading side of the system is infamously tapped out, which is the biggest limiter for increasing service on their whole system. They don't even run that good a rush-hour slate because it risks shorting out the lone 1930's-era substation at Wayne Jct. that props up that whole half of the network They're leaning harder on their less- power-hungry push-pull sets with a cheapo purchase of some used beater single-level coaches retired from Montreal to try to stretch things, since the power-hungrier EMU's end up causing the draw brittleness once they reach a certain set length. Despite the travel-time penalties they have to put up with because of push-pull. They'd have to add multiple new substations and re- phase-break the whole of the system to be able to run :15 service anywhere. It's probably a billion-dollar-plus project (and if they're in the mood to spend that much, they might as well convert from 25 Hz/12.5 kV to 60 Hz/25 kV so at least the substations don't have to be completely custom-ordered at huge blowouts). It's also an incredibly dense stop-spaced system, but it's also almost entirely low-platformed as they to-date have outright refused to move towards any more ADA compliance, repeatedly saying "never" for completion of it as a long-term goal. So the amount of padding in their schedules is unacceptably large for the low-platform dwell delay, and that's likely to interfere bigly with trying to run :15 headways because the schedules won't be precise enough to avoid cascading delays from variable low-platform dwells. That's another problem that'll cost billions just to beat back enough to make a difference. To go along with the system's general state-of-repair being pretty poor and the vehicle-side state-of-repair being abysmal (see: recent crises with the 52-year Silverliner IV fleet being forcibly grounded due to repeated fires).
I guess it's a conversation-starter, and that's all well and good if it lights a fire under people to keep pushing for it. But SEPTA's got to stop being the perennial worst-run transit agency in the U.S., start getting some serious amounts of state funding lined up, and start loading up on real world-practice expertise instead of a revolving door of political hacks if they want a prayer of readying themselves for this. They're actually in many ways much further off than the diesel MBTA network is from true RER/UR readiness despite their preexisting electrification.
No. The feds did not take kindly to floating 80% of the cost of the Center City Connection only to see SEPTA turn around immediately after accepting the money and slash-and-burn their systemwide service levels (including the mass-abandonment of all the diesel lines and the electric lines' further-flung suburban stations), creating a ridership cratering that took 40 full years to reverse. The feds invested in it with the hope that they'd be making efforts to modernize the rest of their system, not burn it all to the ground. When Reagan took office SEPTA was Exhibit A of the supposed unreliability of trying to prop up commuter railroads because they felt like they got punked, so the whole country had to suffer from years of federal disinvestment as a result.
It's why the NSRL debates are going nowhere without firm prerequisite commitments to upgrade the whole system to RER service standards beforehand. Because of course the tunnel is not going to be worth the money if it sits only half-used by current barely-useful Commuter Rail frequencies. There has to be real momentum built and achieved at running the target frequencies before you get the run-thru tunnel if they want to beat the "SEPTA curse". When Seth Moulton was bloviating in his fly-by-night press junket 2 years ago about that never-released Harvard Study reassessment of NSRL, he took the backwards "build then tunnel, THEN get the frequencies" stance (that ran contrary to what the RER advocacy groundswell by TransitMatters et al. were saying), got frequently asked by interviewers "...but what about when SEPTA didn't following through on that?", and then sat there with a dumb look on his face because he had no answer. It still stings and still carries that much disrepute 45 years later what SEPTA did to itself, in spite of getting their tunnel build. We have to do better by actually delivering on some substantial measure of the service levels before the feds are going to trust another prospective RER system with megaproject funding. Which is why it's probably not such a bad thing that we won't have Moulton to kick around any longer. He might've been sincere in wanting NSRL (or might not...he wasn't exactly year-to-year consistent in his advocacy), but he had absolutely no clue how to pitch it to the fence-sitters both in the public and in the government who had well-founded reasons (e.g. the "SEPTA curse") for their skepticism.
