I've done a tad bit more than a napkin drawing and made a real quick 3D model using Roblox (Not the best 3D modeling tool, but it's the only one I know how to use)
I've exported it to OBJ, here it is.
https://www.dropbox.com/s/8awcejv99jgiuql/obj.zip?dl=1 (Direct link)
Some pictures if you, like me, can't figure out what the hell to do with a 3D model:
http://prntscr.com/em2f03http://prntscr.com/em2f26http://prntscr.com/em2f4oIn order from smallest ring to largest ring, there is Live (In the direct center), Neutral (In the second largest ring), and Ground (The largest ring)
There is a plastic bump on the top that is supposed to insert into a notch in the socket, and when turned it would hit a microswitch and turn on the power. Two or more bumps/notches could be added for better locking and stability.
This way, the outlet wouldn't need a shutter, and the plug wouldn't need a sleeve. The power is off until the specially shaped notch is turned and hits a specially shaped microswitch in the socket. So you can stick whatever you want in the outlet, and won't get zapped.
The model isn't to scale by any means. I haven't done any real world measurements or anything, it's just to illustrate the concept.