The purchase was part of a fool’s errand to worsen the ratio of peak to off peak trains that would have hurt SEPTA financially and in terms of its efficacy as a carrier. The densest (in terms of station spacing) commuter railroad in the country had no good reason to buy the heaviest locomotive hauled coaches they could find and only use them at rush hour, all in a crusade against the middle seat, which in all honesty, might get used twice a day. They would have required longer schedules if used on anything besides peak express service, and possibly even still. EMU’s can do everything locomotive hauled equipment can, but not vice versa, and the new leadership seems to get that.
To answer your question, inquiries are out re SILVERLINER VI, an EMU project to replace the now 50 year Silverliner IV equipment. The capacity these cars would have provided really isn’t needed with the shifts in demand, so I would doubt we’ll see an order over 275. Trains are needed at midday and evening when they’re sitting in yards, not at rush hour when mostly everything is rolling.