According to modders who are working on the Switch right now, there is a NES Emulator embedded in the firmware codenamed "flog".
http://switchbrew.org/index.php?title=Title_list
https://twitter.com/AllSourceGaming/status/883085036374851585
This is pretty interesting because so far in Classic Console games the emulator is embedded in the game download. This is the first Nintendo console to include the emulator in the firmware itself, so technically you would only have to download the original ROM from the eShop.