Six months ago, I was firmly in the camp it was going to happen. MCK claimed that Apple was sourcing a 27" MiniLED 5K display that he believed would go into the Mac Pro and Intel had new Xeon CPUs available and AMD was working on the RX 6000 (the "big brother" to the RX 5000 in the new iMac).
There are a mix of things inside and outside of Apple that probably screwed up one last iMac Pro. it could still come if the Mac Pro - iMac Pro Mac Apple SoC isn't due until mid 2022 (or later). Sliding from Q4 2020 into 2021 would be a decent gap filler. Lots of folks have an expectation that the high end Mac transitions are just a matter of a handful of months away instead of toward the very tail end of Apple's transition window. ( That Apple grossly under promised and will over deliver). That exactly the oppsite of their track record in the high end space over the last 7+ years. ( "working hard on new Mac Pro' ... shows up 2+ years later. iMac Pro driffting. 6 years between 2013 and 2019 Mac Pro , etc. ) So when Apple says "two years" , there is pretty good chance the seriously mean that in the Pro transition space.
I wouldn't expect the miniLED stuff but rolling out the iMac Pro with :
Xeon W 2200 series ( or just keeping W 2100 at 2200 series pricing. The price drop is the key issue. Effectively it is already there with moving 10 cores "down" in line up)
Latest Thunderbolt v3 controllers. ( support XDR external display )
Nanotexture screen option for LCD
Navi 2 with HBM
wouldn't be surprising. The iMac Pro would gap the iMac on max memory capacity , max core count ( for those with embarrassingly x86 parallel workloads) , work with XDR (better than the iMac) , gap the iMac on GPU ( again embarrassingly GPGPU parallel workloads ) . All of the T2 NAND is
not soldered down ( end of life data retirement much , much cleaner. Upgrade paths much , much broader. ) .
It wouldn't be the ultimate single thread drag racing machine. But it never was the ultimate single thread drag racing machine.
Navi 2 would probably mean driver availability would slide into 2021 anyway. Apple should have sorted out the ratio of Nanotexture options on the 27" screens by using the iMac demand curves. So that will be much more predictable. If Navi 2 has a HBM option the footprint update on the logical board update is probably pretty minimal ( similar to the minimalistic logic board upgrade did on the 2020 iMac 27" ) . CPPU socket the same , T2 the same , 10GbE the same all minimal impacts. Thunderbolt controller update ... again not much of gap there.
If Intel's timing on Xeon W2300 ( Ice lake / 10nm) version had been better than perhaps would have been on different vector. Same with Navi 2 ( which also is probably late versus circa early 2018 time line estimates; as Navi 1 hiccuped badly late in 2018 .) . The more components slide into 2021 the less work Apple is going to want to do. It really depends upon when Apple 'quit' on Intel and AMD as CPU options. If that overlapped with getting started on "next version" of iMac Pro then probably stuck with small (cheaper ) tweaks to the current design. Basically the kick-the-can to fill the two year gap.
[ Apple rode the Mac Pro 2013 for 6 years. They certainly could ride the iMac Pro for 5 just as cheaply. ]
But in 2021 Apple will have more powerful Apple Silicon SoCs available (A14X and maybe better) along with a custom GPU. If the entry-level Apple Silicon iMac grows to 24 inches, then it's "big brother" will likely have a screen larger than 27 inches.
Available for the laptops in 2021. Sure. For the top end desktops, that is a bit dubious. Apple is probably going to want to wait for an even more mature process to do relatively much larger dies.
An Apple SoC that can handle x20 PCI-e lanes isn't necessarily in same boat as on that does over x64 . Previous Apple SoC haven't even done anywhere near the 16-20 range.
Apple may even try to cover the 24" iMac with just an iGPU ( Apple GPU) and there isn't even x16 lanes. the 24" model probably isn't going to be the biggest "GPU" possible any more than the 21.5" is now. What Apple is likley trying to cover there is more so in the "good enough" range. That means the 24" and 27" iMac may not share the same SoC ( and not arrive in a close time window. ) . Hence the 27" Intel refresh now to kick the can much deeper into 2021.
The 2020 iMac is almost as powerful as the entry-level iMac Pro and fairly cheaper. Also there was no technical reason for Apple not to add Nanotexture glass as an option on the iMac Pro, yet they didn't even though one would think it would be more appealing to that market than the iMac. Apple also did not increase the storage tiers for the iMac Pro to match the iMac.
different tools for different jobs. The storage tier thing is more than relativity lame because how many folks are even buying Apple 8TB SSD at those prices? It is very much a lazy thing they Apple could differ until later to help put "better lipstick on a pig" of a minimal upgrade that they want to slap a "New" label on in the web line up marketing page. Same with the Nanotexture. Those two coupled with a substantive GPU bump could get a "New" label. If they split those into different groups that is a much tougher spin.
So I am starting to seriously think the "big brother" Apple Silicon iMac could be the new "iMac Pro" to complement the 24-inch "iMac".
It seems doubtful that Apple is going to make the Mac Pro SoC just for the kinds of volumes that the Mac Pro would generate ( presuming the price point on the Mac Pro starts at roughly the same starting point). An All-in-One to increase the sales volume of the Mac Pro SoC would make lots of sense economically. Apple could chop down the core count and/or clock to drive some segmentation with the same die ( and leave a gob of unused PCI-e pins or pads ) that would still be the "wider core count workloads" would still be the gap between the regular iMac and the iMac Pro. Similarly throw a non 27" screen at the iMac Pro ( 32" and 6K and definitely have a bigger gap of not huge drama to get industrial design to croak out a different enclosure for the system. One of the major boat anchors on the iMac Pro is that it "has to" share practically the same exact baseline design with the mainstream 27" model. Decouple them and there is obviously more room for something else. ).