No. Just... no.
NCR has no business on the east coast. BoS and Enclave was semi-beliveable, due to the former's mission of grabbing tech and the latter's mission of re-establishing the US Government. The East Coast would be an obvious choice for both groups if they wrote off the West Coast as "almost done" or "too prickly right now."
But why would the NCR be on the east coast? First, they'd have to crawl through hostile territory, whether or not they won the Dam or the legion's leadership is non-existant. Assuming they get through that, most of the US is still largely a wasteland with settlements here and there, with things what will kill you as soon as look at you. Finally, they'd have to have a really good reason to leapfrog over to the east coast. The Lewis and Clark expidition was made in part because the United States gained ownership over a large parcel of land and had no idea what was in it.