During the April 2017 pow-wow
"... With regards to the Mac Pro, ....and we want to architect it so that we can keep it fresh with regular improvements, and we’re committed to making it our highest-end, high throughput desktop system, designed for our demanding pro customers. ... "
https://techcrunch.com/2017/04/06/t...-john-ternus-on-the-state-of-apples-pro-macs/
Some folks have 'spun' thing into the highest possible throughput on the market. IMHO, that is a misread. It is "making it our highest" which more likely means fastest throughput in Mac product line up. A single x16 PCI-e v3 standard slot would do that. They don't need to engage in a slot count war to get there.
later one there is also this:
"... But certainly flexibility and our flexibility to keep it current and upgraded. We need an architecture that can deliver across a wide dynamic range of performance and that we can efficiently keep it up to date with the best technologies over years. ..."
The Mac Pro doesn't have to be solely about 'highest' everything (i.e., most expensive possible. ). The system has to cover a broad range also.
Again many folks have spun 'efficiently keep up' to be equivalent to 'have to keep up with the computer parts bin a Fry's' . There is no direct commitment to that. That relies on the presumption that Apple is gong to commit to the absolute minimal amount of work. ( they have laid a track record for that certainly, but that hasn't been highly successful either. ). With a reasonable amount of resource allocation and active work Apple can keep up to speed.
Apple needs to "talk" by delivering product. What Apple needs is an architecture where they can update a major subsystem on a regular basis (e.g., 12-18 months ).
" ... We’re not going to make any promise, or anything that should be misinterpreted as ‘Here’s what Apple said they’re going to do in the future on the Mac Pro.’ I will point out that we make decisions at a product-by-product level ... Just because on one product we remove something doesn’t mean we’re going to remove it from everything if it doesn’t make sense. So there’s no reason to draw any conclusion. For example, [saying] what we choose to do on a MacBook Pro means that that’s all we will do on a desktop in the future. That’s not a reasonable conclusion. We make choices based on a variety of factors per product."
This was right after a joke about no Macs with RS 232 port and Serial ATA (SATA) port.
One of those factors is likely going toward where folks are going to. So RS 232 is a port won't see. IF $/GB was exactly same for PCI-e SSDs , then SATA would be in the same bucket. All the aspects are going to be put under scrutiny.
In the April 2018 discussion
"...
This time around, Boger was succinct: the promised Mac Pro will be a 2019 product.
“We want to be transparent and communicate openly with our pro community, so we want them to know that the Mac Pro is a 2019 product. It’s not something for this year.” ... "
https://techcrunch.com/2018/04/05/apples-2019-imac-pro-will-be-shaped-by-workflows/
They aren't looking to slide into 2020 or to pick parts which could highly likely cause them to slide into 2020. It is quite likely they expected to finish a substantive amount of work in 2018. How far into 2019 isn't hinted, but it is a definitely not ship in 2018.
I think the title of this second article is a bit off though.
"... Because we want to provide complete pro solutions, not just deliver big hardware, which we’re doing and we did it with iMac Pro. But look at everything holistically.” ... "
That "Pro Workflow " group isn't primarily about Mac Pro. That is an aspect, but so is enhancing the pro software on MBP and iMacs. It isn't about making software faster by just throwing more Watts and 'grunt' at it so that it is only effective on the largest wattage Mac we sell.
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they have used expansion, but they also haven't excluded thunderbolt from expansion either. One of the more common complaints made about the iMac by detractors is that they don't want the monitor/screen attached to the computer. So an alternative to that is modular. They would have 'checked' one of the big box complaints.
Apple didn't get off of slots for RAM and CPUs on the current iteration. Two fans are in the iMac Pro.

It is probably a larger power budget more so than fans ( fans follow with need to get rid of the heat from the power usage. )
the "Pre Workflow" isn't about the Mac Pro specifically. It is about all the Mac that are in the Pro space. The Mac Pro is and would extremely likely remain a small signal digital member of that space. How Pro software works on MBP, iMac , and iMac Pro is just as much of a charter of that group as anything that runs on Mac Pro. It is a fairly wide and broad space, so know they don't know all the answers for all time there.
Keeping the product updated doesn't necessarily conflict with end user updates. They have done RAM. They don't actively support CPU, but folks have done it.
I think the bigger disconnect is those who primarily look at the Mac Pro as something that is primarily just a container in which to put commodity "stuff". Apple's view is more likely aligned with the Mac Pro as a working system for work now first, something that is a nexus (e.g. hook monitor to it), and something that can be adjusted, within some limits, later.