Are you a GPU user or a Mac User, Apple will provide what Pro Mac users need (SOTA GPUs) with timed upgrades, maybe those upgrades will require you to visit Apple's service centers and/or buy a propietary GPU (with Apple's markup), if you are crying to self upgrade GPUs with Amazon or Fry's sourced cards,Respectfully I think you dont belong here.
There are two markets for the Mac Pro - people who buy a machine, and never upgrade it, and people who buy a machine and upgrade it themselves.
The first is evidenced by the large number of cheesegraters that were never upgraded, largely because they are never taken out of service, and just do the same thing, especially in print design where requirements have been largely static for a decade, day in day out. Also, most of the tasks they did, are now capable of being done with cheaper hardware. The 2013 Mac Pro possibly suited these people, but was probably overkill for their needs.
There are not enough of them on their own, to sustain a dedicated machine. The iMac Pro is a design that was IMHO committed to manufacture before this became apparent.
The second group wanted a mac that was user-servicable, and user upgradable, and despite claims of there not being many GPU upgrades etc, during the time the cheesegrater was current, there were 3rd party cards for it - right up until 2012 Nvidia had current "mac edition" Quadros for them. This market is freelancers who do their own tech, or small shops that have an inhouse tech / sysadmin (speaking from experience as sysadmin for a <20 employee movie / tv commercial company that did shoots all around the world, for markets all around the world, I maintained an edit & design suite with a pair of g5 powermacs + xserve, plus the company's fleet of powerbooks, tape backups etc). An hour downtime for a hardware upgrade was something that had to be scheduled. There was no hope in hell of ever getting the OK to take a machine offsite for however many days it would take Apple to upgrade it (anyone thinking this will be a while-you-wait service is reality-challenged - you'll have to accept whatever appointment they give you from opening to closing, 2 weeks in advance).
There are not enough of those people, on their own, to sustain a dedicated machine.
A machine that suits the second group, left alone and not upgraded, also suits the first
with no downsides for anyone, aside from being a bit larger than a machine dedicated to the first group. It has a hope of being a self-sustaining market.
This mythical market you're suggesting - people who want to upgrade a "pro" machine, will happily have days of downtime or put up with the genius bar appointment schedule, but don't want to do it themselves,
does not exist. I can't for the life of my figure out if you're actually in favour of this idea, or just trying to be a devil's advocate.
And respectfully, given the Mac Pro has had 5 generations of user-upgradable slotbox, and only one generation of locked-down sealed appliance, it's that viewpoint which is the odd one out / minority / "doesn't belong here".
