I'm sure the only reason AA hasn't done it yet is the lack of IT resources to bolt the logic onto their ancient systems. AA has been last to implement a number of customer-unfriendly enhancements for that reason.
I for one have found DL's award pricing to be pretty good for certain domestic routes. For example, you can't get below 25K AA miles for a longer domestic roundtrip unless you have an AA CC and your destination is on the list of deplorables qualifying for reduced mileage awards. But I have snagged AUS-DTW and AUS-BOS on DL for 15-20K miles roundtrip in Y and 30K in F. And I got nonstops for my troubles. Overall the awards may get more expensive but the variable pricing can create some valuable nuggets that would otherwise be unavailable.