I simply can't grok the use case for this, sorry. When I hear the terms "Unix" and "Cross Platform" uttered in the same sentence, I reflexively think about cygwin.
I think the use case is similar to Python's os library. You will probably still need to write specific code for specific systems (for example, Windows' paths vs Unix's paths), however it still makes things easier for the programmer since you can use the same interface between multiple OS.
I'm not sure why I would use this over Midipix[0] since it allows me to use standard POSIX APIs.