Cuphead was heard to be only releasing on Xbox One and Windows Store, but it seems that this is not the case. StudioMDHR confirmed on NeoGAF that the PC version of Cuphead will be launching on Steam and GOG, not just on Windows Store.
“Yes, this Cuphead game is exclusive to Xbox and PC (with Steam and Win10 versions at launch and a GoG release likely shortly after). There will likely be a Mac version down the road and possibly a Linux version beyond that (unless we lose our houses or whatever).
We own the Cuphead IP.”
The post also shows that there might be a possibility that Cuphead will also launch on Mac OS and Linx soon if they want to pursue it.
“Cuphead is a classic run and gun action game heavily focused on boss battles. Inspired by cartoons of the 1930s, the visuals and audio are painstakingly created with the same techniques of the era, i.e. traditional hand drawn cel animation, watercolor backgrounds, and original jazz recordings.”