Project Giant Robot was a prototype shown by Nintendo's Shigeru Miyamoto alongside Star Fox Zero and Star Fox Guard at E3 2014. The game saw you control giant robots, destroying buildings by swinging the Wii U GamePad. Project Giant Robot was continuously referred to as in development in various financial reports, but was omitted in the most recent one.
Polygon reached out to Nintendo about it and they confirmed it had been cancelled "after considering our overall product and development strategy". No massive guess to think it has something to do with the shift from Wii U to Switch and for a project that used the GamePad so heavily that seems to have spelled the end.