You can actually launch FNF as a Non-Steam game if you download the files for the game and add the Funkin' file to the non-steam game launcher. You can then type "./Funkin" into the launch options without quotes and then boom! the game should launch for you.
Of course, you won't need to do this unless your a Linux user like me and don't really feel like using the terminal to launch the file. Other than that though, an official Steam release would be nice!