While I can't speak specifically to AA's internal decision, I can make some educated guesses. The A220 is likely to be around for a while -- it has a very long range (transcon) and is very fuel efficient. It's still quite possible -- even likely -- that AA will acquire A220's at some point. It is definitely a mainline plane. DL's are configured with 12F/97Y, which is a bit small for AA's taste. I would assume that AA would look to acquire some of the stretched version, which I believe will seat about 20 more passengers or so. Actually, it might make a good replacement for older A319's! So, I wouldn't count out the possible of seeing the A220 in AA's colors eventually.