I'm willing to bet that there will be some time taken up by the localizations on both the 3DS and Switch, on the NA and EU directs. So, in order to fill that time up, Nintendo of Japan will focus on new game releases (much more exciting).
Then again, they might just focus on confirmed releases like Snack World...
Assuming this is a half-hour Direct, then Splatoon and ARMS should take up three-fourths of the Direct. The rest will be a showcase for the Switch and its upcoming lineup (reminders of, say, Disgaea 5 Complete releasing or a multitude of indies), and localizations for the 3DS (Miitopia? pretty much anything from Atlus?)

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:3







