The future of one idea to improve New York Penn Station’s hellish rush hour overcrowding will have to wait until the future, said experts at a forum held at NYU Monday. The concept, called “through running,” has been proposed by two advocacy groups. But it got a thumbs down for the present time, said a consultant who studied the idea for Amtrak and the Long Island RailRoad, and NJ Transit. Through running is a largely European concept that has express commuter trains stop, and allows for drop-off or pick-up from widened platforms. Then, trains move on to serve the metro region across agency bo…