If the freight has dwindled to close to nothing, they could run non-FRA equipment on a time separation basis. Such as European equipment or even railbuses. Still have the same or more worry about grade crossing crashes. Or since they aren't running "west" of Brunswick they could use midwest style bilevels with low boarding platforms and still achieve handicap access.
That sounds like a needlessly expensive idea, coupled with the fact that the only two platforms that exist on the route are hi-level, including the one in Bath that is a temporary setup on a trailer.
A couple of regular passenger cars is good enough for a service that hasn't moved beyond trial runs. There's frankly no need to spend money the operation can't sustain on oddball equipment.