I don't think it will cause problems for mainline DL
If I'm not mistaken, Song is replacing Delta on some routes, so there is mainline DL
shrinking. In other markets, such as some out of DFW
, mainline is disappearing and being replaced by DL
Connection with more frequencies. This frees up aircraft to replace the aircraft going to Song. Delta is shrinking capacity on some routes, taking 757 to 737-800 and 737-800/MD-88 to 737-200. It appears that while 757s go to Song, they are replaced with smaller aircraft, and those smaller aircraft are replaced with even smaller aircraft operating more frequently (DL Connection).