Spawning multiple instances of applications via shortcuts
you can open a file from the terminal by using the open command. For example to open the Atom editor you could type open -a /Applications/Atom.app/Contents/MacOS/atom. To open another instance of the app, use the -n option with open. For example, to open another instance of Atom type: open -n -a /Applications/Atom.app/Contents/MacOS/atom.

I suppose a script could be written to execute this and then a keyboard shortcut for the script could be set.