Originally, the Silverliner V was supposed to be a modified BBD M7, running off catenary and with "long doors" with steps and trapdoors, actually. That was before SEPTA went on its re-bidding crusade in an attempt to save money on the purchase.
Pity that NJT wouldn't consider joining in with SEPTA insofar as getting new EMUs anyway—the all-Comets all the time situation isn't helping things too well, and I'm sure that more than just a few commuters would be interested in seeing Arrow IVs on the rails...