Hmm external piping-be interesting install, not sure Im picturing as faucets are thru the wall or sink/counter. But yes the valve is direct to the shower head.
If I had room as some, and I looked, I would have installed a self contained exterior shower box on side of cabinet. Be a clean install, the other 23 1/2 hours of the day all that would be visible is the door.
DiskDoctr: single lever shower valve? Look in the TCU thread, there are a couple of really nice shower valve installs. As to maintaining the temp-using the shower head is closest, though I can turn ours off-immediately back on and temp drops. Using the faucet youve got the water setting in hose that cools off, plus our diverter would reset? Where recirculation would be nice-at least water in lines up too faucet would stay hot. Ive not seen any faucets that mixture could be kept with separate flow on/off. Even if, once water stops flowing temp changes.