If they do an exchange, they'll order in a 1st gen from their warehouse.
Of course, if you have a car crash preventing you from getting there to pick it up on the day they told you to, called to let them know you'd be there the next week, and arrived to discover that it had been given to someone else, and were very, very nice to the cute Genius boy you *might* get a brand new 2nd gen... though I doubt lightning strikes twice...
(loving the external vol controls, btw)