Almost a year later than first expected, Apple has finally added indoor maps for Japan on iOS 11 and iOS 12. Narita Airport (Chiba) and Chubu Airport (Nagoya) are the kickoff points for what is hopefully going to be a continuous rollout. Major airports like Haneda and stations such as Tokyo and Shinjuku are still AWOL and the iOS Feature Availability list has not been updated yet.
One of the problems that Apple Maps faces in Japan is that multiple agencies hold different indoor map data sources. Shinjuku station for example is a collection of 4 different railway companies and more than 3 subway lines. Collecting and coordinating a complete robust data set takes time.
Apple Maps Japan is still missing some other major services available in other areas: traffic, lane guidance and speed limits. It will be interesting to see if the Apple Maps makeover gets any mention during the September 12 event.