First of all the elephant in the room that nobody is really discussing is that they are switching to Frontier style brutally uncomfortable seats. Those seats are rock hard and kill your back for any flight (or delay) over 2 hours.

Which leads me to the next point. I prefer to be the last person to board a plane (I don't need bin space). With the new awful seats and with seat assignments, there is no incentive at all to being the first to board, so there will be folks jockeying to be last at the closing window whatever it is, 10 or 15 min before departure. Trust me, this already happens on Frontier. (there's an added bonus here in that if you are last to board you just take any empty seat which might be better than your assigned one--yeah they tell you not to, but rarely is it enforced.) Gone forever will be the days when Southwest might have a plane fully loaded and ready to go at 10 or more minutes before scheduled departure.