You do not seem to have read the article ... unless you have insights into the Apple design process, there is no where stated anything about modular design.
The Mac Pro they talk about will be extremely upgradable.
Actually "modular design" is in the first sentence you posted. :-)
I have a fairly high level of interest in this and have read a few articles. A different one had a lot more quotes from the Apple folk, among them:
As part of doing a new Mac Pro it is, by definition, a modular system we will be doing a Pro display as well. Now you wont see any of those products this year; were in the process of that. We think its really important to create something great for our pro customers who want a Mac Pro modular system, and thatll take longer than this year to do. - Apple Senior Vice President of Worldwide Marketing Phil Schillerhttps://techcrunch.com/2017/04/04/apple-pushes-the-reset-button-on-the-mac-pro/