if you did that and you put in a BYOD SIM from ST i'm willing to bet dollars to donuts that you dont have access to the Cellular Data Network menu (ST SIM cards register as "unknown AT&T", then force the phone to load the ATT_US carrier profile) and are therefore stuck in the same boat as everyone else using a GSM iPhone on ST.
It might be the same boat but most of the people in that boat seem to be pretty happy with their situation. I just wonder if it will have a SIM slot at all or be a Sprint iP5. There's speculation that Sprint has been unable to sell those millions of iPhones they bought and will soon offer them on VM. I wonder if they might have also sold a boatload to Walmart to use on ST?
I'm sure it's a pipe dream but if these were VZW with LTE it would be a spectacular deal and I would be standing in line to buy one. Of course, the day VZW (or AT&T) allows LTE on an MVNO is probably a cold day in hell.