There's a difference between upscaling and emulating the game at a higher internal resolution. Twilight Princess on Shield is not upscaled, it runs internally at 1080p. Upscaling is just a pretty way of saying that an inferior resolution image has been stretched across a higher resolution display with some bells and whistles in play to make it look nicer than it would if it was just plainly stretched, but that's not the case at all here. The game DOES run at 1080p on the Nvidia Shield.
There's a ice article here that explains the difference between un-upscaled 1080p source on 4K versus 1080p source upscaled to 4K versus native 4K display. http://www.red.com/learn/red-101/upscaled-1080P-vs-4K
Twilight Princess on Shield runs at native 1080p through emulation, even though the game wasn't a 1080p game originally. It is NOT upscaled. Same thing as how N64 games on Wii and Wii U Virtual Console run at native 480p even when they originally ran only at 240p on their original console. And should Gamecube games or Wii games come to Switch, the fact that Twilight Princess can run at native 1080p on the Shield while emulated means that the Switch could do the exact same thing since both pieces of hardware are basically identical.
Granted, that's still not the same as a full on remake with nicer textures and gameplay tweaked to accomodate the possibly different methods of input, but saying they're "upscaled" is downplaying it. The fact that they run at native full HD for games of that vintage is quite a big deal. It means you could get on your Switch the same kind of great results you could get on PCs running these game on an emulator like Dolphin, which during the days of the Wii made everyone wish these games were running at 1080p on the Wii itself, even with the same textures and all, making possible VC re-releases on Switch without any further enhancements already much better offerings than the originals.