According to a well recognized Nintendo hacker, a title called "Mario & Luigi: Superstar Saga DX" was recently added to the Nintendo eShop server.
https://twitter.com/SciresM/status/858162826711490561
There's no more info on the title yet, but a potential announcement could be coming soon.
Edit:
https://twitter.com/SciresM/status/858162826711490561
There's no more info on the title yet, but a potential announcement could be coming soon.
Edit:
Icon also leaked
The final name of the game is Mario & Luigi: Superstar Saga + Bowser's Minions