Not even thinking of changing seats. Same as the current planes. Only, if you purchase the economy additional seats, the airline (or consolidator) blocks the middle seat from sale.Maybe you have a little table that fits over the arm rests, maybe not. Essentially this is what sells in Europe as Business class.

So someone who can't afford first because the price difference is usually so high over what they pay for economy, this will give them some extra space but be priced more reasonably.