Southwest to add weekly Saturday flight to Ft. Lauderdale for Winter.
https://www.boston.com/travel/travel/2019/05/31/southwest-adding-nonstop-service-to-fort-lauderdale
They're only going toe deep, with infrequent flights for only a month and a half.
There is already a bunch of competition on that route. Spirit, Jetblue, and Delta all fly there. Plus you have AA and Delta flying to MIA (lots of overlap with FLL), and Jetblue and Delta to PBI.
Though the Boston to South Florida market is huge, so there might be room for one more carrier.