People overestimate how a modern Mac Pro tower would work. A Mac Pro tower is not going to permit hackintosh-style hardware builds. They will force the use of w

People overestimate how a modern Mac Pro tower would work. A Mac Pro tower is not going to permit hackintosh-style hardware builds. They will force the use of whitelisted "supported" hardware, and sell it all themselves with their standard high markups. Without proprietary hardware, there is not enough money in the market for them to bother with a tower in the first place. It would also put the "it just works" aspect of the Apple brand at risk, should customers use 3rd-party hardware components that wind up not functioning properly due to unofficial drivers. Apple has a public image to maintain, and they will not expose themselves to having customers claim that their Mac Pro "isn't working", blaming Apple instead of looking to the 3rd-party hardware manufacturer.