This isn't at all unusual, when Apple first switched to Intel chips they followed Intel's upgrade path every six to nine months pretty faithfully.
The past few years that has been derailed partially because Intel has fallen behind on its own timeline and partially because Apple has focused less on the Mac and more on the products and service that make it the most money.
A 10 bit, 500 nit, 5K screen by itself would cost around $1,500, before you even get to the CPU or GPU which themselves are expensive.
For those speaking ill of this configuration, who here honestly could make productive use of or even afford a computer with 18 cores, be it Mac or PC.
Apple has already stated a new Mac Pro is coming but not this year.
Five Thirty Eight works in probable statistics - its not fortune telling.
Predicting the most likely outcome, as you see Donald Trump's chances of winning weren't zero, just not as likely.
A very good article from a friend of mine who is on the inside of this issue.
The market for those who swap internal hardware components at this point is so small, Apple doesn't have to support that desire - most people just buy a new computer.