Datapoint: I just applied for my second US Air MC, and was instantly approved. I had gotten my first card back in April, 2012, and was instantly approved then as well. The first card is still open. I did not have to call the reconsideration line and give them an excuse for the second card.
The online system also allowed me to add the new card to my existing online account instantly. It showed both cards on the existing online account, and even gave me the last 4 digits of the new card to differentiate the accounts.
Now I hope to get a second opportunity at the 15k bonus miles if I spend $750 per month for 3 months!
Thanks!
