This article lays out the CEO's reasoning. I'll bet that Jet Blue, the holdout will also fold. Thus, no guarantees anywhere last forever
Since I transferred 120,000 Marriott reward points to SWA and then got a free companion pass for my wife, and we fly out of Phoenix, SWA is our first choice because we fly for just the ticket tax. I have long believed that SWA will someday charge for bags and that is why we have learned to fly with just one carry-on, for up to 7 days.
I'm hoping Southwest and Jetblue will keep their free bag policies. I'm not a huge fan of Southwest but will use them if they can offer me a direct flight for the right price. I do however love Jetblue and wished their route map was a little larger. I find myself using Delta mostly and get free bags with them since I have a Delta Amex. Because of the latest Marriott partnership with United I'm now also able to get free bags with them as well. It's nice to have free bag options when picking flights.