A patent by Nintendo has been unearthed that appears to show a Game Boy cover for an electronic device, such as a smartphone. The patent was filed with the United States Patent and Trademark Office in March 2018 and describes an attachable cover with operation buttons. Drawings included with the patent application look just like the iconic Game Boy console.
https://www.notebookcheck.net/Nintendo-patents-Game-Boy-cover-for-smart-devices.337280.0.html