There should be nothing technically preventing Apple from doing a future "step-down" model in the same case that has a smaller power supply and less PCI slots and tops out with the 16-core W-3245M and a mid-range video card (Vega 64-class) that starts at $4000 for the 8-core with 32GB, 512TB SSD and "entry-level" video.
If massively chopping down on slots and capping at 16 cores there isn't much need for the W-3200 series. The W-2100 series topped out at 18 cores; which is greater than 16 so could cover that anyway. The "extra" x16 is tossed when you toss the additional slots.
If Intel follows up with a W-2200 the pricing on the W-3200 in the overlapping core count range probably isn't going to work too well. ( current snapshot core
ercentage : 8:11% , 12:27% , 16:48% , 24:2% , 28:11% ) 8-12 cores is a critical block to make the product "work".
While probably not the best sampling demographic but
this thread about how many cores do you want.
basically will be a "Mac Pro" killer because most folks only want 16 cores or less. Apple has to "suck in" the 8-10 core folks that want slots in to make the top quarter of Mac Pro target market viable.
That would also highly overlap with the iMac Pro. So deeply eating into both probably makes it a non starter. The iMac Pro has the "hate all in ones" differentiation factor so the overlap there is way less.
Then they can have the current design for the "big jobs" starting with 24 cores, 128GB, 1TB and mid-range video for whatever ($8000?) that can then scale to the five figures with 28+ cores, terrabytes of RAM and SSD storage and multiple top-end video cards.
24 cores and up barely makes it into the double digits percentage. It is pretty close to "nobody". Remember the Mac Pro only has a single digit of the Mac market. 10% of a single digital is quite likely less than a single digit.
2009-2013 ... Mac Pro was in single digits range back then too. So this isn't a "chicken and egg" thing that Mac Pro is going to bust back up into double digits again. It isn't, even with this new system. Which is probably primarily why Apple has stuck a "low volume" tax on it. Nor
The real hold-up will just be the will to do so. And considering how Tim likes to have products for all niches (why he keeps stuff around that should have been End of Life years prior), I'd argue if anyone would do it, it would be him.
This "fill lots of niches" notion doesn't really hold up. Tim is more of a fan of selling the previous , older, "now cheaper to make" model than Jobs was. Lots more products got "Steve'd" in Jobs day because the limit on Mac models was held pretty rigidly small. If something "new" came then something "old" had to go. Cook has allowed more older stuff to float for longer periods of time. Examples: MBP 13" 2012 for about 2-3 years after "Retina" models came. The iPhone 5 in tweaked forms of 5C , SE . The entry level iPad with two year old series processors. Recently the MBA retina while what is effectively almost 3 year old MBA "classic" floated at the $999 point.
Almost none of the entries aren't a "new niche" filling. There is substantive possible fratricide at the 13" laptop level but if Cook was looking to fill lots of niches there would be twice as many Mac , iPhone models as there are now.