FYI - I just received a $90 additional credit, on the 50K + $50 offer, because the amex system couldn't grant me a temporary credit limit. No idea if it was a specific issue tied to my account or larger system issue that Delta/Amex is currently having.
I went to make a r/t booking on Delta's website for March 2016 while not logged into my Skymiles account. 50K + $50 offer for 2k spend appeared after selecting outgoing and return flights. Applied and was instantly approved, but the approval message also included the following: "Unfortunately, we cannot provide you with a temporary credit limit . . . . Since you were unable to use your temporary credit limit,
we will be awarding you $90 in the form of a statement
credit. You will receive this statement credit within 8-12
weeks on your Credit Card."