I really don't know but the prospect of a fusion of Windows Phone 8.1 or 9 with Windows RT (or at least the global app thing or whatever they call it) should be a good reason to develop something.
Also, I have tested a lot of the music apps for Windows Phone 8.1 and most of them lack features Android users regard as standards, really basic stuff, and these apps aren't even free.
So, a good app could make good money.
Music Bee 3; EAC; MP3Tag; Music on Synology NAS 115; Logitech Media Server on RPI 3; RPI 2 with Hifiberry; Poweramp for Android/Lineage