Unfortunately I can see more and more airlines going this route in the future, it has already been heading this direction over the past decade.
Frankly Frontier and Spirit probably don't care all that much. They are making good money and people are still buying tickets. That ticket price online looks pretty good until you factor in the nickle and diming.
As far as boarding goes while I am not a huge fan of the Southwest open seating it does tend to get people boarded quicker. You do run into the traffic jam situation every once in a while though with people swapping seats.