Upon further research, NW operated MSP-FLL with a 319 summer 2008 (DL utilized a 320 this year) and suspended the route that September. They resumed service that fall with the 319 (DL intends on operating the 320 this year) and transitioned to a 320 and 757 for the holiday season (DL's planning a M90 & 757).

Comparing 2008 (NW's last as a truly independent company) and 2012, DL operated a very similar schedule -- with a slight increase in capacity.

Thus, DL hasn't made any significant changes to this route.

And FWIW -- September's slow season into Florida. Throughout most of the 2000s, one could travel to Florida for RT$100-$200 throughout the country. Significant capacity reductions have changed that; of which MSP has been immune to.