Even with the billions of dollars Apple has in the bank the absolute quickest they could turn around what you are describing would be 9 months at a guess. ATP

Even with the billions of dollars Apple has in the bank the absolute quickest they could turn around what you are describing would be 9 months at a guess. ATP guess around 200,000 Mac Pros are sold a year - the first year of a new version after so long could easily be 1 million units. Getting that production and logistics line set up is a big undertaking even if using old cases etc. For the extra 6-9 months that a new design would take it's totally worth it for them as will hopefully give them a modern design that is good for 5-10 years that meets the needs of the 2017+ pro market, using a chassis that was designed for the 2008+ needs would be a step back for Apple and pros in general. Apple like to push the envelope and while they certainly do make mistakes (I count the trash can as a mistake but not the Touch Bar) there's no point in them going ultra conservative.