If I was an airline changing from an all Airbus fleet to an all Boeing fleet I would want Boeing to pick up the costs of introducing the new fleet which would give a substantial discount off the list price. If that order was converted into a sale and leaseback it would leave the discount for fleet transition that could be paid in cash and fund new investment in the airline. However the costs of introducing the new fleet would now have to be taken as a provision against future profits. It would mean cash now but create future liabilities. Anyone with an interest in the strength of the balance sheet, such as the CAA, would probably be misled and probably not very happy.