I have not decided how that should be handled yet.
There are three way to handle that. Open an instance of the program for every dropped file or send all files as parameters to the program or only accept the first of the dropped files.
Most program does not support opening multiple files. For example try dragging two files and dropping on Notepad then notepad will not open any of them.
I thinking that there need to be an option on the launch item where it can be configured how that item should handle multiple dropped files.