Delta's route network is such that turboprops (ATRs and Q300/400s) seem perfect for many routes currently flown by regional jets.

Next-generation ATR42/72-600s would be perfect for many of the sub-250nm segments out of Atlanta, with the faster Q400 for routes up to 400-500nm.

Passengers might not like them whirly thingies on the wing, but they'll probably like them less if the alternative is a more expensive ticket.