So ... you add seats with no intention of selling them, to improve your chance of selling one at £500 at the last minute?!

Great idea except a) you can already leave some empty seats via yield management, b) even if strong of bladder and low of height (to fit in the new loo) that person is likely to know that his £500 last minute seat will get him a middle seat beyond row 12 with an increased chance of his carry-on being forcibly removed and book elsewhere .....