Nothing is confirmed until an official announcement, but sinonobu noticed that on the Japanese Nintendo Direct page a slot opened up about a week before the last direct aired. tonyh24613 provided evidence that this isn't a new pattern and that he'd noticed the same phenomenon before. Today, another slot opened up in the same manner.
So apparantly there's another empty spot on nintendo direct page...
Guessing Stars is coming
Just before April's Nintendo Direct, the JP Nintendo Direct page had an empty spot.
Apparently JP Nintendo Direct site has an empty spot again so there might be Nintendo Direct soon
For anyone curious:
April 30 (archived)
Looks like they moved the Miitopia direct.
Pokemon Direct was moved last time. This was exactly one week before the April Direct.
If it's happening, expect an announcement this week.
I found this once before.
And there was a direct on Nov 13, announced on 10.