It's utter madness. Replacing a perfectly good fleet, with a fleet that does exactly the same only with requiring a vast amount of money to introduce when there's nothing wrong with the the current fleet. If the A321 is too big, switch to A320s. If the A320 is too small, spaceflex them and refit to 186Y which is only 3 seats less than the 737-800. You'll need to operate A LOT of full flights to make it worth all of the extra expense just to fly an additional three seats around.