Dragging something on a running app's Dash icon should reveal it's application window(s)
Currently, it is impossible to do drag and drop from a maximized application to an unmaximized one, as starting a drag action in the former brings it to the front and hides all other windows. Windows allows me to solve this issue by dragging the object in question over the destination app's taskbar icon, which reveal it's window after a few moments.
It would be nice if the Dash would allow something similar for icons of running apps. If the app has multiple windows open, the user could either be given a choice of windows (as in Windows 7/8) or the last app's last focused window could be shown (which is probably a good heuristic for most use cases).