The MAX may have some cockpit design limitations, but Boeing is being responsive to their customers: The new model MUST be included in the common type rating and the buyers demand it. I'm not privy to Boeing's decision making, but this just has to be a biggie for their major customers. What airline wants to retrain all of their 737 pilots against an entirely new type rating, when a short 'changes' course will do. I strongly suspect that Airbus is taking the same course with their NEW edition of the 320 series - and for the same reasons.