JR East made an update regarding their switch to the E257 series EMU for the Odoriko service, they also posted some pictures for the renewed interior as well. The two E261 sets for the new Saphir Odoriko service were also delivered recently and were seen doing test runs.
https://www.jreast.co.jp/press/2019/yokohama/20191128_y01.pdfSo there'll be 13 9-car sets (-2000) and 4 5-car sets (-2500) for a total of 137 cars, that pretty much means that some of the surplus E257-500 sets used for the Uchibo / Sobo limited express services will be converted as well
In addition, they'll also build 8 KiHa E120 DMU cars to replace the aging KiHa 40 DMUs for the Tadami Line
>>1423809Even without taking freight trains into consideration, it seems like they'll also make prolonged stops on certain stations along the route for entertainment / goods peddling purposes
https://www.westjr.co.jp/press/article/items/191120_00_ginga.pdf 