I am planning to do the Alpine route on the opening day, April 15, 2017. I hope that opening dats is as reliable as everything else in Japan as I don't have a lot of date flexibility! Will be doing it starting at Shinano Omachi, which is readily reachable from where I will spend the night before, Matsumoto.

Note that apparently details (like schedules) of the 2017 season apparently won't appear on the website until 30 days before the opening date.