And the irony is, the focus in BNA is a remnant of AA's hub at BNA.. and there were nonstop MEM-BNA flights in those days.

Most of the frequently flying residents in MEM are deep into DL's frequent flyer program, if for no other reason than their NW accruals were changed into DL accruals. It won't be easy for another carrier to win over those customers... although WN will probably try to invade opportunistically and win share, just as WN did at RDU, BNA, and SJC when AA de-hubbed.