Welcome to the DonationCoder site, goldencut.
ANY feedback would be nice at this point - it's too complicated, it's impossible, it's been done already, it's stupid... anything... -goldencut
While I like your idea, what you're asking for is a lot more complicated than you might think.
First of all, anything you write is, technically,
outside of Windows Explorer. This mean that a developer will have to consider all the different versions of Windows Explorer (2000/XP/Vista/W7/W8 + 32/64-bit of each) along with all of their different capabilities, limitations and idiosyncrasies. Furthermore, the shell context menu has its own set of capabilities, limitations and idiosyncrasies to deal with across the different Windows versions as well. It's a real mess.
Let's say you decide to do this anyway. Now you have to deal with the fact that your interface is separate from your playback engine which, in and of itself, isn't a bad thing. However, in this case, you don't have access to the innards of the interface so you're forced to use an intermediary, i.e. a service, API calls, window messages, etc. This can be very limiting and very frustrating to work with. For what it's worth, I've written an audio player called
Trout that some folks here at DC have come to like. I could not imagine trying to write such a player without designing, and having full access to the user interface code, myself.
I hope this made some semblance of sense. =]