I wouldn't expect the next JetBlue...LCC to come out for another decade or so. The problem with a new LCC, is that now, SWA and JB have the guns to blow them out of the water. Between the legacies and the LCC's don't expect them to take competition laying down.
Once SWA has built itself into Legacy status and then give it another decade there might be a new LCC. So that could be as far off as 20 years.
Remember after dereg there were a lot of carriers that came out, but only AWA exists as the same entity.
But that is only history and as much as history is bound to repeat itself, it is just as bound not to repeat itself. Historically, speaking, SWA should have never made it, but they seem to be doing just fine.