According to JR Central, the peak of crowding for this winter holidays (December 28, 2017 to January 4, 2018) will be on December 29 for outbound trains and on January 3 for inbound ones. The following data are from this site Shinkansen Timetable’s independent survey. The seat availability changes from moment to moment, but they maybe of some help to find remained seats.
In November, this site Shinkansen Timetable had been visited 130 thousand times by 96 thousand users, and the page view was 342 thousand. The28.0% in the total access was through desktop, 66.4% through mobile, 5.6% through tablet.
JR East and West released the all night train services in Tokyo and Osaka area will be available from Dec 31, 2017 to January 1, 2018.
According to this site Shinkansen Timetable’s independent survey, the train congestion peaks during coming winter holidays (December 28, 2017 to January 4, 2018) will be the outbound trains on December 29 and 30, and the inbound ones on January 3 because many users search the travel plans here for these days. It is our private study. The official estimation based on the actual sales of reservation tickets will be released around the same time as last year, that was December 15, by JR Companies.
JR West will release unlimited-ride ticket for the coming new year day, January 1, 2018. It is “Ganjitsu JR West Norihodai Ticket 2018” (元日・JR西日本乗り放題きっぷ2018), which allows unlimited travel on whole of JR West lines, Chizu Express lines and JR West Miyajima Ferry. There are two types of tickets; for ordinary class ticket allows to reserve seats up to six times during the travel and for Green-car ones allows to take Green cars seats up to six times.