In some sense, I did have that- my electronic boarding pass was saved to my iPhone wallet, and it doesn't update unless you do it. So I actually checked on the FRA-DTW flight and verified it was still there in case push came to shove. But it wouldn't do a lot of good (I'd imagine) if the flight was full and they really did give away my seat. Which they didn't, of course, and it was reassuring to hear above that Delta rarely removes you from a flight unless it's been cancelled or something. I would at least like the option to try and make tight connections- I'm generally pretty fast through the process getting back into the US.

Keith