Steps to reproduce:
1. Download attached project
2. Run it on Windows Phone 8.1 or Windows Store Apps ARM device
3. Change quality settings to see difference.

Why this was not fixed?
This is a by-design change from 5.0, "Windows Store/Phone: Shadows on mobile devices there now work just like on iOS/Android - no cascaded shadow maps (i.e. not "too slow on mobile" anymore)."

Now they work just like on all other mobile platforms (e.g. iOS/Android) - meaning there's no cascaded shadow maps, and they are at acceptable performance (instead of being "horribly too slow for any real game").

To reduce pixellation: use shorter shadow distance in quality settings; use larger shadowmap resolution; set light to use "soft shadows"