I don't think making commuter rail trains stop as if they were metrorail makes sense. They serve different functions. MARC will never get the headways at the proposed stops to make "don't look at the schedule" transit a feasible reality, and the extra stops slow down commuters that want to use the line for its original purpose as a DC to Baltimore rail service.

I would definitely love to see what you are proposing though, if we could see that kind of Penn line frequency with that short of a travel time it would be huge for the Maryland economy. But understand that adding stations and more stops is directly contrary to having fast trains between two major hubs.

I don't think its infeasible to eventually widen the NEC to enable local metro trains, but its a really, really far off project we probably can't see realized in our lifetimes. It would have to come after so much other stuff is done - the red and yellow lines, the green line extension, etc. Unless Amtrak and the fed wants to pay for it.