You can already drag files into the drop area of the "Open File" dialog.
Adding drag&drop support to the whole NI application isn't difficult to implement, but it wouldn't always work because it needs a dedicated GUI component to listen to d&d events. It's easy in Notepad since there is only a single edit window. However, NI uses all kinds of components, depending on which resource you have currently selected. It would probably only work reliably if you drag the files onto the resource tree, menu bar or status bar.
I can add this option if you can live with these limitations.
Edited by Argent77, 26 December 2015 - 11:44 AM.