And they do, as long as it fits under the seat in front of you.
I doubt NK is going under anytime soon.

The bigger picture question is whether this step in un-bundling is enough to shift booking trends. US eventually backed down on their charging for water and sodas in Y. Then again, Spirit has held fast to that revenue stream.

But consumers are pretty consistent in splitting their travel purchase habits into two distinct categories: the time of the ticket purchase and the day of travel. As long as they think they got a deal in phase one and didn't get hurt too badly when violated in phase two they'll continue that pattern. Only once consumers actually manage to put the numbers together and see the overall costs as a single number will the patterns have any potential to change. FWIW, CO takes advantage of this same behavioral pattern to offer the "buy up to first" fare difference sales on your reservations. And CO customers are loving it, at least the ones sitting in F are.