I'd expect more punitive carryon/checked bag fees. $20/25 is too soft. Spirit charges ~30/40 range. Refundable fares will disappear. Complimentary water (in a cup) will not be offered. Only for sale food and drink. We'll probably get higher density sardine can seating.

I'm curious if they will come up with creative new fees.

On the bright side, itcould add more routes with obvious low fares that Southwest and the legacies don't offer.

Will Frontier lose their own forum here at FT? Spirit doesn't have a forum. It's just one "Spirit -- some more observations" thread in the Other North & South America Frequent Flyer Programs.