Zooming out for a second, I think Apple has, from the very beginning of the Macintosh, always been shuffling between several competing philosophies of what the Mac is/is for.
On the one hand, beginning with the original 128k, Apple has often conceptualized the Mac as more appliance than modular computer. You buy it and use it; when you need different/more capability you buy another Mac. The Mac as an all-in-one form factor has reached iconic status in the public consciousness. On the other hand, beginning with the Mac II, Apple has also continued to sell some form of modular desktop Mac, often (though not always) marketed more towards professionals. Never as modular as PCs, but offering many of the same types of upgrades. They never really settled on one or the other approach.
On top of that, the Mac has always been a 'premium' product in terms of cost (if you weren't around then, just look at all those 'adjusted for inflation' MSRPs of early Mac models on Wikipedia!
). Those of us (myself included) who have been annoyed for decades at the lack of upgrade flexibility can vouch for the fact that in a certain sense nothing has really changed since the beginning - Macs have always been expensive and have always been less easy to modify and upgrade.
So in a sense this is an unresolved conversation that has been going on since 1984.
Beyond the design philosophy discussion, the additional wrinkle is that since 1984 the desktop computer itself has gone from being the core of Apple's business to an also-ran, verging on niche-market product. The company as it exists today is driven by mobile and wearable computing - product sectors where upgradeability is either of secondary importance or not even a thing.
You could reasonably conclude from this mini-history that the product Apple is
least likely to produce in the future is a more affordable and/or more modular desktop computer, even though they have yet to abandon the modular desktop concept.