Long analisys about Intel CPU (mostly failed attempts to hold Ryzen Pace), buy no single logic reasoning about why an AMD Ryzen based Mac is not possible.
I've touched on AMD elsewhere but, if you must, here's the latest iteration of my feelings on AMD in Macs:
I'll start with technological reasons:
a. Why make it easy for AMD Hackintosh users? Even though Apple will almost certainly be adding the T2 CPU to the mix.
b. What about Thunderbolt? Yes AMD are now allowed to use it but why would Apple want to mess around with their implementation?
c. Yes, lots of PCIe lanes internally, threads to spare and values for money, but Intel are competitive and can offer Apple discounts.
d. For high performance computing surely Intel's AVX instructions will give it an edge in certain video encoding style workloads?
e. Intel's mobile stuff, which Apple show the highest interest in, is just better than anything that AMD has come up with because it also has to pay attention to heat and power consumption.
f. Apple have shown no interest in HEDT - High End Desktop. Threadrippers in particular make Intel stuff look positively parsimonious for power and heat. And as above they like to use Thunderbolt. The big factor here is the sheer heat produced being incompatible with Apple's thin enclosure designs.
g. Going with AMD would surely spell the end of upgradable RAM in the 27" iMac as Ryzen is famously sensitive and reliant on the right kind of RAM for performance reasons.
h. I think Apple are more likely to be thinking of ARM CPUs in 12" MacBooks rather than worrying about engineering AMD into the Apple ecosystem.
And now for the Financial/Marketing reasons:
1. Even without the Intel marketing discounts for Intel Inside stickers etc, Apple have to be getting some big discounts from Intel for CPUs. The impact of Apple leaving for AMD would be massive and many have assumed that the Beta leaks are a strong-arm tactic to get leverage on Intel for future discussions. The effect of AMD's strong offerings in the market has forced many price cuts for Intel - something Apple will be keen to use.
2. While AMD are great value for desktop PCs, it's in the mobile market where Apple make 80% of their Mac sales - Intel CPUs are a massive proven quantity vs AMD's recent moves in that area and battery life will be hugely important (if not mores than performance). It would be a massive marketing win for AMD if Apple went to them for laptops as well and could lose Intel much more than physical revenue.
3. If Apple were to go AMD, they would have to switch everything that's not Xeon for economy of scale. For desktop users, they can't be seen to have benchmark differentials between iMac and Mac mini - hence why the thread mentions both of Apple's non-Pro desktops getting refreshed at the same time. While this may appear to support a switch to AMD for desktop use, that would then put a question mark over an iMac Pro unless it was powered by a Threadripper which then begins to heap the shade on the just-released Mac Pro.
4. Supply chain - can AMD sustain the next 5 generations in terms of year on year improvements and deliver in the quantities that Apple demands? Apple have been stung before with product that's unavailable.
Kuo rumors point to keep iMac Pro at 27" with micro led, but it doesn't prevent Apple to build an 32" 6k iMac Pro too just based on pro display HDR, but it will be very expensive, likely to start close to 10K.
If Apple moves to AMD Zen from next gen iMac, Mac mini, likely at the same time an IMac Pro loaded with Threadripper CPU will be escorted by an epyc based cheese grater Mac Pro the same quarter.
As you say, such a set-up would be unaffordable and would undermine the Mac Pro.
But let's look at the Mac mini.
The Mac mini in particular can't accommodate Ryzen because most of them don't come with a GPU and the 65w TDP can't really be compared to Intel's own TDP measure which is going up for the higher end SKUs. Either way, unless the Mini uses H class mobile CPUs Apple would have to redesign the case - and is there any small motherboard that they could use to accommodate CPU, iGPU, and 4 Thunderbolt ports?
The Ryzen 5 3400G is probably the most suitable CPU for Apple to use and that's only 4 cores/8 threads and (despite the name, isn't even Zen 2 architecture) whereas the i5 2018 Mini is already 6 cores and, with Comet Lake, would have 12 threads too if Apple refreshed with that.
Apple would almost certainly have to solder the RAM or supply 16Gb as standard as using 'cheap' RAM on these seriously dents graphics performance and can take upwards of 2Gb from system memory which again would be a reduction in resources.
The GPU from the Ryzen 5 3400g and probably the 4400g later this year (sporting 11 Vega Compute Units) would probably beat the HD630 but the whole system would probably lose out in overall compute benchmarks.
If Apple chose to go with these CPUs - they would have to find a suitable motherboard chipset that comes with Thunderbolt controllers (the 3400g apparently comes with 20 PCIe lanes, 4 more than Intel) and a cooling solution that can manage it.
It would be a very strange combination of high end Thunderbolt ports and low end CPU - and after all that an AMD 2020 Mini is in danger of becoming less interesting to our Colo friends.
Why would Apple choose to use this CPU in anything other than a poverty spec iMac? it could replace the non-retina 21.5" iMac but would Apple get anything like the amount of orders sorted for this SKU when higher end Ryzens (with 24 PCIe lanes available) would go into just about every other iMac SKU?
Perhaps Apple may find SKUs within the retail Ryzen range - the Ryzen 9 has up to 16 cores and 32 threads for example - but they couldn't use the Threadripper without undermining the Mac Pro.
The Mac Pro may have begun development before AMD's high end CPUs became available - perhaps there might be scope for something in the future.
