This method of operation is now - alas! - mostly out of fashion here in Britain, but it will suit the NEC and its Virginia extensions very well. The unit trains get the job done, but at a price - even in electric mode the underfloor motors are a distraction.Good points!
Even previously, there were the New England Expresses that originated and terminated in New York. They were assigned a separate engine at the other end to drag them into and out of Penn Station from/to Sunnyside. They were detached/attached at Penn Station.
Once Amtrak gets double ended train sets from the current RFP, all these issue will go away. It might even be possible to run through trains from Albany towards Washington DC, since reversal at Penn Station will become a non issue.