> Why would you think Tamachi station will be served in the first place??? > It's not like Keihin-Touhoku will be the line running through. The physical branch point will be close to Tamachi, even though trains to the airport will only stop at Shimbashi and Shinagawa, At least I think that's what the post meant.
Ideally, there would be branching/switching tracks from the Oshio Freight Line to the Tokaido Main Line around Tamachi. However, the spur to the Oi Shinkansen Depot gets in the way. 大汐短絡線 may end up running underground, cutting below the Tokaido Shinkansen tracks.
Photo credit:
http://building-pc.cocolog-nifty.com/helicopter/2015/05/post-c0aa.html 