Re: more than software
Actually, their original plan was for the 737MAX to be a shrunk-down Dreamliner using the same composite build. This would have been great...sleek, modern and efficient..
But American Airlines didn't like that as they wanted a plane that their 737 pilots could fly without re-certification, and a smaller 787 would be a different type. So we got the MAX instead. Yay.
Look up "Project Yellowstone" to see what could have been...