During Tim Cook’s trip here Japanese media reported October 25 (local time) as the Apple Pay Japan launch/iOS 10.1 release date. This is confirmed with the major Apple Pay partners going down for system maintenance that day. Both Docomo iD and JR East Suica will be completely down for “unscheduled system maintenance” the early morning hours of October 25.
iOS 10.1 is confirmed as a requirement for using Apple Pay in Japan.
Check the Apple Pay Japan Intro Q&A for Apple Pay details.
10/19: updated with Suica system maintenance information.