Asriel on 12 June 2017
I expect any 3DS reveals/news will be done during Treehouse. Hopefully "a number of reveals and first-looks" translates to more than revealing Mario/Rabbids and a first-look at Zelda DLC and Fire Emblem Switch. I'm expecting Animal Crossing for 2018 and a Smash Deluxe port, but I'm not sure beyond that how much 'new' stuff there'll be for Switch.
I'm expecting Mario & Luigi Superstar Saga remake to be announced for 3DS during Treehouse, and am still hoping (probably in vain) for Link's Awakening 3D to be announced for 3DS.
