Random implementation-related thoughts...
I guess that somehow MPH would need to know or become aware of paths of appropriate starting programs (e.g. if a player is launched via a batch file, the path of that batch file). FWIW, I wouldn't mind specifying such information in an ini file
If MPH did have that info, may be upon receiving a hotkey, if it found no players running corresponding to the hotkey, it could start the top-most matching player.