I guess since the entire tour is a stadium tour it wont be a case of putting parts of an arena stage into a stadium like the Joanne tour, or fitting a stage designed for a specific theatre onto whatever stage a company had paid for her to perform on. Maybe they waited to announced Tokyo to make sure it was logistically doable once the stage was finalised? The rumoured dates from 2020 have now all turned out to be true, the only exception being Singapore, so presumably they planned it with the intention of getting production over to Japan.