The Nintendo Switch Online service is due sometime in the second half of September, which means that a significant firmware update will be arriving soon to accommodate it. Those who subscribe to Nintendo Switch Online will be able to back up their saves online, so a firmware update is necessary.
Dataminers have discovered that the 6.0 firmware update for the Nintendo Switch has already been uploaded to Nintendo's servers, which has allowed them to find out what is being added. A user on Reddit named OatmealDome has posted his findings, which has revealed what we can expect in the upcoming firmware update for the Nintendo Switch.
The 6.0 firmware update for the Nintendo Switch will add support for the Nintendo Switch Online service and grant you the ability to back-up your saves. The update will also be adding some Captain Toad icons, as well as adding some new anti-piracy support.
The most interesting find in the 6.0 firmware update is a selection of new controller icons that are being added to the Home menu. If you are using a specific controller on the Nintendo Switch, such as a single Joy-Con, then you will see that controller on the menu when you press the Home button.
The new controller icons include images for the Famicom controller (both the regular ones and the one with the microphone built into it), a Nintendo Entertainment System controller, and a Super Nintendo controller.
We know for a fact that twenty Nintendo Entertainment System games will be available for free to subscribers of the Nintendo Switch Online service, and the official website claims that more games are going to be added regularly, which means that we may see titles from other Nintendo consoles.
It's possible that Nintendo is planning on releasing their own wireless NES/SNES controller that can be used with their free games.
Nintendo had previously released a Super Nintendo controller for the Wii that could be connected to a Wiimote and used wirelessly. Nintendo also isn't shy about releasing lots of controllers for their system, as their two biggest upcoming games this year (Pokémon Let's Go Pikachu & Let's Go Eevee and Super Smash Bros. Ultimate) have their own custom controllers being released alongside them.
There are already wireless NES/SNES controllers available for the Nintendo Switch that are produced by third-party retailers, so Nintendo may have seen these and decided to get in on the action.