The back of the Shuffle says: Model No.:A1204 EMC No.: 2125 5V 1A.
Let's take it apart!
The top and bottom of the shuffle have white plastic caps held on by mild adhesive. Heat the caps with a hair dryer and gently pry them both up. Make sure you don't pry the metal beneath the caps up at the same time.
Remove the shuffle / loop switch and the power switch.
The shuffle / loop switch is actually a metal arm about .5" long that extends along the bottom to a switch on the logic board in the center of the shuffle.
Use a spudger to lift out the metal retaining brackets on either side of the Shuffle. The hinge side contains a tiny extension that supports the casing, so start from the other side (as shown).
Apple includes a 'flash guide' with ten different codes. The LEDs flash green, amber, and red.
Apple has done an impressive job of packing functionality into the headphone jack. The dock plug has three conductive strips, plus the ground post. It's safe to assume that the plug is multi-modal and switches between USB, analog audio, and possibly power modes. The separate power mode may not be necessary if they can get enough juice off a 4 conductor USB connection.
It should be easy for a third-party developer to make a small USB adapter that restores the memory-stick functionality of the Shuffle.
Notable features: Li-ion polymer battery (this is soldered onto the logic board), headphone / dock / power jack, and memory chip (hidden beneath the headphone jack.