One game that we know is in development for the Nintendo Switch but has yet be formally announced by Ubisoft and Nintendo is Mario X Rabbids. An image has popped up online purporting to be from the game which is likely to make its debut at E3 next month in Los Angeles. We shall know for sure if it is legitimate in just a few weeks time.
Update: Updated with key-art work in image header.
Thanks, N-Dub Nation and Maxim