Just to clarify, not having Drag and Drop is not an API limitation (see [1]). Rather, they haven't implemented it yet in every place you'd expect to see it.
[1]: https://msdn.microsoft.com/en-us/library/windows/apps/mt2276...
[1]: https://msdn.microsoft.com/en-us/library/windows/apps/mt2276...
I also remember reading somewhere that the problem exists only when drag and drop is done between modern apps and win32 apps.