Ah, the conundrum of a seat for every passenger vs. increased capacity. Of course, if BART was actually designed competently, you would have passing tracks at stations and thus be able to have a variety of services to match passenger demand and needs (i.e. expresses, skip stop services, zone commuter expresses, etc.). Then you would have trains with comfy seats for services serving the outer suburbs, and the high capacity ones w/less seating on the locals or inner services, as BART, though nominally a subway, is also a suburban commuter line.