JR East, in commemoration with the 156th anniversary of the opening of Yokohama Port, is running a special train using the 651 series on May 30th from Mito to Ishikawacho Station in Yokohama and return. The train will use the Ueno-Tokyo Line and traverse the normally freight-only Takashima freight line between Tsurumi and Sakuragicho. It'll be interesting to see where the 651 series trainset will be stabled after dropping off its passengers at Ishikawacho Station before its return trip to Mito (Negishi Station sidings?)
JR East pamphlet:
http://www.jreast.co.jp/ekitabi/tabitetsu/common/pdf/201505/15051102.pdf
Old video from front of a 185 series (apparently the same rinji ressha service as the one to run on the 30th), on the Takashima Freight Line: