A new unannounced SNES controller was spotted by Restera user Link83. This was found by the user setting up an alert for any new Nintendo FCC filings. Not many details were found outside of the rear of the controller due to the label location and it appears to be in the shape of the SNES controller.
This has led to speculation that SNES games will be added to the Switch Online service in the near future, which has only offered NES games so far.
Other third parties already offer a great option for SNES controllers like 8bitdo, but this does seem like the typical progression for SNES roms to make their way onto the Switch via the online service.