NVIDIA released its orginal Shield back in 2013, and then launched a series of tablets and TV boxes under the Shield branding. Earlier rumors indicated that NVIDIA were working on a new Shield, but nothing has really happened even if Nintendo has revealed its Switch console.
According to The Verge, NVIDIA submitted documents of its second-generation Shield to the FCC on July 15th, 2016, but somehow decided to cancel the product finally.
Nintendo has adopted a custom Tegra processor for the Switch, just like the Shield. Both models should have been competitors. However, it seems NVIDIA has ditched it due to some reasons that only the company is aware of.
Actually, the market orientation of Shield is kind of embarassing, since the smartphones can play all the games that Shield can, and consoles of other brands have their own exclusive gaming titles.