[rootusrootus]

Double, more or less, if the sole requirement was to have the same revenue per flight for a full plane. E.g. a small short haul aircraft with, say, 35 rows of economy class (six across) would end up with 30 rows of first class (four across). That cuts capacity by about half.

But some people will pay more for comfort. And most regular people are incredibly price sensitive, they'll suffer quite a lot just to save even 10 bucks on an airline ticket, so your hypothetical airline doing this strategy went bankrupt.