DL to DTW or ATL (ATL is a big market for F9) may not be a bad idea though Delta would have to learn from its mistakes it made when it served TTN in 2006. They served both Atlanta and Boston using the CRJ-200 (Boston service at the end was Beech 1900s). The problem, they charged too much to fly out of TTN. They thought they could gain a premium on service when they couldn't. Flights were always $150-300 more than EWR or PHL.