Homebrewers have discovered an NES emulator hidden within the Nintendo Switch's firmware, according to a recent update to the group's wiki. SwitchBrew is a wiki resource for Nintendo Switch homebrewers, and as of June 28 it updated to include the emulator system application. According to the update, the emulator is referenced as "flog" in the firmware and is currently completely unused by the Nintendo Switch or any of its games.
The NES emulator is technically included on every single retail Nintendo Switch and has likely been there since the console launched. The NES Classic that so many were disappointed was discontinued could be hidden within the Nintendo Switch, if Nintendo so chose.
In all seriousness, an NES emulator isn't a particularly robust system application. Nintendo could very well have included "flog" on the Switch simply because it could. It's difficult to draw any meaningful conclusions from it being on the console.
Nintendo likely does have plans for the NES emulator eventually, or at least NES games in general if not the emulator itself. While Nintendo has yet to reveal any official Switch Virtual Console details, the service's inclusion on the system is an inevitability. And if the Virtual Console isn't what uses flog, then the emulator will more than likely be used as part of Nintendo's online account system for the Switch.
Paying for Nintendo Switch Online, which will be required to play online multiplayer games when the service eventually launches, will also come with access to a Classic Game Library. The games shown so far for the library include NES games like Super Mario Bros. 3 and Dr. Mario.
For perspective's sake, the Wii U Virtual Console had over 90 Nintendo Entertainment System games available for purchase. That's over 90 games Nintendo has previously been willing to and able to sell to consumers via Virtual Console, at least on the Wii U. Knowing that the Nintendo Switch should be able to provide a similar service right now makes the situation a bit odd, but Nintendo is well known for creating such situations.
The lack of NES games could be the result of the curious success of the NES Classic or the forthcoming plans for the Classic Game Library. But all that likely matters to consumers right now is that could be available and aren't.
The Nintendo Switch is currently available for purchase, though is currently out of stock at most retailers.