I realize that with Amtrak's funding crisis, any capital for service expansion is not to be expected. However, in a fantasy world where money was available, what would be the drawback of using part of the now-closed GM assembly plant in Linden as an Autotrain northern terminal? I know that the DC tunnels cannot support autoracks, however, there must be some reasonable alternate routing that can be considered.
The GM location would require a minimum investment to support the service. The rail infrastructure is in place, including facilities to support automobile loading. You can beat the location, rail-wise, right next to the NEC. Market access is huge and Linden is situated next to many highways serving the NY/NJ metro area. As it currently stands, what should be a 5-hour drive to Lorton from NJ ends up taking 7 to 8 hours on a good day, and this likely serves to turn away NY/NJ customers.
GM-Linden is likely a brownfield site. There are funding sources available to reclaim brownfield sites for new uses. Linden has built enough big box stores across the street (Route 1) to preclude any retail development of the site.
Finally, I do recall an effort by Autotrain in the 1970s (not sure if it was part of Amtrak at that time) to locate a terminal in the NY/NJ area. At one point, the old Staten Island Railroad Terminal yard in Cranford was being considered, but was ultimately rejected due to NIMBY opposition.