If anything, MEM does not have enough flights to have a successful rolling hub schedule. A rolling hub would require a lot more flights (not just four per day [if even] to various destinations). MEM does not have enough O&D to have a rolling hub schedule (just like STL for AA).

It might work for MSP & DTW, but it won't for MEM. NW has one intercontinental flight out of MEM. That in itself basically forces the flights to come and go in banks if there were to be any connecting traffic.