Well if you consider the need for a sound card, an SDI I/O card, potentially a M.2 raid card, a dedicated GPU (depending on support) we’re all out of slots should the availability be reduced.
There are zero macOS on Apple Silicon drivers for a discrete GPU card so not sure why counting that slot as used here. That is not on the likely possible path. So even in this example there is a likely empty slot. Part of the trade off in making a "system on a chip" is that some stuff goes into the SoC. The upside to that is that it frees up PCI-e slots. Some folks will point to it as a negative, but it has two sides.
In the Mac Pro (2008-2012) slot survey ( which is limited demographic sampling, but something concrete to looking at. ) there were there were about at least as many occurrences of two GPU set ups than one GPU ones. One of those GPUs was typically tagged as the "boot" GPU because it was a officially supported card by Apple and presented a hack-free access to a boot screen. If the "boot GPU' is in the SoC that too has the upside of freeing a slot.
Afterburner card soaking up a slot ... gone with M2 era SoC.
The computational deficient of a 2022+ era M2 generation SoC to a couple of 8-10 year old DSP processor is going to be what for the average small , limited budget home studio?
Apple has been skimming use cases that would have strictly required a Mac Pro in 2008-2009 into other Mac products over the last decade. That is only accelerating with the move to the M-series SoCs. Those SoC don't have to cover "everything" to peel off more than decent sized percentages.
I happen to think that the cost of the 2019 MacPro is heart breaking because I personally can’t afford one and believe it is mainly driven by the enormous cost of the Xeon processor. But the industrial design throughout is near perfect.
It isn't driven by the Xeon processor. The entry Mac Pro 2019 has a 8 core W-3223
Intel® Xeon® W-3223 Processor (16.5M Cache, 3.50 GHz) quick reference with specifications, features, and technologies.
www.intel.com
The tray price for that is about $750 and Apple has around a 30% mark-up on that so $975. $390/$5999 == 16.3% . It is
less than 20% of the system cost. Even if throw in the DIMM slot costs that are likely not being used it likely still under 20%. The chipset that is required with the processor.
https://www.intel.com/content/www/u...l-c621-chipset/specifications.html?wapkw=c621
$61 . Plus mark up is $80 . So processor+"have to buy chipset" is 18% of total system price. There is still 80% of the cost that is just not the immediate processor costs.
If the Xeon W-3223 processor+chipset cost was zero a $4,999 Mac Pro still would have been a 66% increase over the $2,999 starting point for the MP 2013 (with a Xeon E5v2 processor in it).
Pointing that the hyper costs for the 24-28 core models is not where the main driver for the 100% entry price comes from. That is just misdirection. Additionally, hand waving at ECC RAM isn't doing it either (apple's mark up on RAM is even more ).
That double sided , relatively very large, complex circuit layout motherboard probably costs almost as much as the entry processor does. Can try to blame that on the processor for that, but that is a stretch.
Apple just has a "low volume" tax on the Mac Pro. The volume of systems sold in and of itself probably isn't interesting financially to Apple. Back in the 2009-2012 era there was a CPU daughter card that allowed the same chassis to service folks who just needed a limited number of DIMM slots and one CPU package and those who needed lots of DIMMs slots and two CPU packages with just one product across a relative (for a Mac product) wide range of prices. The 2019 takes those "max DIMM slot , double CPU package" entry prices and puts a single CPU package solution to for. The iMac Pro - 2020 iMac more so the pricing point for the old school single CPU folks. Extremely likely Apple knew that was going to lead to less "Mac Pro" sold and hence the "low volume" tax.
I would just hate to see what has been such a design and engineering success for professionals after the flop and admittedly personal purchase of the MacPro 2009 for them to make a repeat on account of the the Apple Silicon allowing them to reduce the size.
The whole entire history of the general PC industry has been amount doing more with computers that were smaller size. Started off with don't need mini or mainframe computer to do work. Has shifted to laptops can do work previously classified as "desktop only required" . Now folks have personal computers in their hand. Saying the size can't shrink any lower than 'xyz' is largely a form over function viewpoint.
It is 100% not a repeat if go back to the same number of slots the 2009 had. Zero slots of MP 2013 and 1-4 of a new Mac Pro is a change. If it is only one , then it id not much of a change, but it would not be retreated back to what they did in 2013. If 3-4 slots then pragmatically it is the same as what was there, that was a viable product.
Also just because the "tower" Mac Pro gets smaller doesn't necessarily mean the "rack" Mac Pro would get smaller. Reducing the width of a "rack" model make it harder to rack since the rack rail distance is standard. If exactly half the width Apple could build a special rail chassis that took two of these. The would get give slightly less "bad" rack density (still way off Mini's density for most rack use cases) . Or Apple could take a half size 1-4 board and add on a 2-4 expansion board to flush out the missing rack width.
If the folks with abnormally high number of cards are highly correlated with rack models then there is about zero design and engineering success 'loss' there. It won't be cheap. Rack is $500 increase now. Probably could go up $800-1000 increase ( not shifting costs to users who never use that many slots. Have to self pay) . But Apple isn't aiming at folks with low budgets.
Apple stated at the Mac Studio intro that the more common configuration for the Mac Pro was a 16 core and W5700. That means the double W6800 duos and 28 core options are likely way outside the norm. Sell too few and Apple is likely not going to stay in that category.
I’d buy a MacPro the size of a wardrobe if it meant I could do all the things in a Mac environment.
Toward the beginning of your response you effectively said you would not. Lament the current price and then say will buy something that Apple would highly likely charge even more money for you would buy. Goes back to folks who wished that Apple sold a 'slot box" xMac for $1,599-2,399. They didn't with Intel. They even less likely to do that now ( the Mx , Mx Pro , Mx Max provision no substantive PCI-e lanes to do that at all. ).
The Mini , iMac, and lower 'half' of the Studio are being provisioned with laptop optimized SoCs. Apple has detached themselves from the general desktop PC market support for the R&D for a mainstream desktop So C (e.g., desktop Ryzen 7000 or desktop i9-i7 Gen 12 ) . over 70+ % of what Apple Macs sold are laptops so that is where the focus is. That leaves the Mac Pro way, way , way out on an island. It isn't going to be a 'low cost' island.
Apple's mid range is going to get covered by laptop optimized SoCs. That ship has sailed.
I doubt "half size" Mac Pro would drop the cost much at all. The highly custom , relatively very low volume Apple SoC that go into the upper half of the Mac Pro line up are going to be expensive. More likely Apple will crank up the minimal RAM and SSD storage capacities to keep the $5,999 (or higher ) base price on the next Mac Pro. That will help the perceived value proposition a bit. Apple price anchors the remaining Mac Pro users at $5,999 with an Intel model and then 2-4 years later come with M-series model at the same price point. They don't have to ask the remaining folks to adjust their spend much at all.
If Microsoft wants to do this, they’ll be taking it the whole way themselves, without Apple’s help. And sure, Apple wouldn’t mind but, if Microsoft were to go to that effort to get their OS to run on Apple’s hardware, there might be some upset OEMs, the ones that have gone out of their way to create systems designed to run Windows ARM. 
www.macrumors.com
arstechnica.com
www.sonnettech.com
