Didn't mean to be critical of anyone's specific ideas. I spent so much time doodling subway maps and dreaming about transformation that I stupidly convinced myself to go to grad school for urban planning, so to everyone smart enough to ponder these things without incurring 70 grand in loan debt, cheers to you!
I'm chiming in because I know how exciting it is to think big, and my time in school and then in related work since has led me to the conclusion that it's better to filter those ideas through the lens of what the actual monetary, political, and civic capacity is (a coping mechanism to avoid ongoing disappointment and permanent urban planning blue balls, if you'll pardon the term).
I mentioned platform lengthening because it's something SEPTA itself is already thinking about, not because I thought anyone was suggesting it here. It's a good example of one of the realities of US transit planning: agencies tend to try and solve the problems they know they already have, rather than proactively build for the problems they one day hope to have. SEPTA is dealing with the problem of today: the MFL is at or above capacity, and apparently running with greater frequency is an issue, though no one in a position to know has ever explained to me why 3-4 minutes is the tightest headway the line can achieve. Point being, SEPTA would rather spend money on fitting more people onto every existing train by elongating platforms to uniformly accommodate longer trains than it would to build one new station that would serve a more specific and limited population that frankly isn't YET that big (though presumably development will fill in CC west of 20th enough to eventually create that very real problem).
Read about platform lengthening here and you'll note a little issue: it's MASSIVELY more expensive than lay people would ever possibly conceive it might be.
http://septa.org/strategic-plan/reports/fy-2020-cap-budget-2020-2031-program.pdf
We can debate whether $1.3 BILLION DOLLARS is well spent to make every el train two cars longer, but accepting for a moment that that's what it costs, and accepting for a moment that it's already worked into SEPTA's budget as a real and previously agreed upon priority, the point is that they'd need to finish spending $1.3B on this before even thinking about other MFL investments. By the time they finish this (if they even can), it will also be time to think about replacing the entire MFL fleet, which went into service when I was a kid, so they'd probably have to put that ahead of new stations as a priority too. That's also an opportunity - if they bought articulated trains without separated cars as seen in Paris and other places, they could potentially avoid lengthening every platform and just educate people on when to walk forward to exit at shorter stations - but I digress.
I'd love for SEPTA and US transit agencies to act more like those in Europe and Asia by planning proactively for future capacity and anticipated growth. Unfortunately, they aren't in a position to do that because the money isn't there to keep stuff going at a state of good repair, let alone build new. Perhaps enough climate-related crises will compel the feds to drastically shift how they allocate and prioritize transpo funding in the coming decade or two. I would love that (not the crisis part, just the reprioritization part). In the meantime, I'm intentionally limiting my expectations to avoid disappointment and hoping that a combination of MFL capacity enhancement, smart procurement of higher-capacity trolleys, and expedited construction of nicer and new underground connections between lines makes the existing less-than-ideal multi-seat ride situation that much better.
(I know this whole thing belongs in the Transportation thread, apologies for prolonging the non-real estate discussion).