The iPad uses a "hand me down" SoC.
Compared to the top of the line iPad Pro
https://www.apple.com/ipad/compare/?device1=ipad-pro-12-9&device2=ipad
it is two generations older ( A10 versus A12Z ). It is currently 3 back from the iPhone. And by mid October it will be 4 generations back. ( probably won't iterate to A11 or A12 until Spring 2021 ).
Not only is it more than a couple generations back it is the "hand me down" from a much higher volume product line. iPhones sell in the triple digit millions. The Mac Apple Silicon will not.
The A10 is cheaper because it is already paid for and fabricated on older equipment with far lower relative demand ( compared to wafer starts available. )
The tech screen is old. The touch ID old. the camera gimped (relative the leading edge ).
Individual Mac models will sell in much lower volume that iPads do. ( even iPad Pro is group them together since they use the exact same processor not matter what the screen size varies to in each generation. ). The Apple Silicon SoCs are going to be more expensive to make in part they will sell in lower volumes. Scale matters when it comes to custom silicon cost/price.
The iPads also only support two USB ports (one through the new fancy optional keyboard, but nominally just one USB port). Basically limited video out. ( primarily focused on being wireless only ). Macs , with rare exception in modern era, support multiple Thunderbolt ports. Also discrete GPUs in some configurations. High double digit ( if not triple digit ) RAM capacities.
The Developer Transition Kit (DTK) doesn't have to be a real Mac because it will never be sold. It just has to run some general apps in the mean time until there are realized products for sale.
(and it is running an iPad Pro part , not an iPad part. )
The whole notion that the 'use old parts to hit the lowest price point" , $329 iPad should be used as prince anchor for a Mac price expectation level is just grossly flawed. Apple isn't going to be out to sell the oldest possible hardware that they can get away with in the new Macs. The iOS/iPadOS product line ups have the "sell older generation models at lower prices " strategy. The Mac product line up doesn't have that general rule.
When new Mac comes out in a category then the old one is discontinued. ( there are some rare corner cases like the MBP 13" 2012 non-retina. But Apple had the new Retina line up that was really the "new" MBPs. ) There hasn't been a Mac product update where Apple jumped to an 2-3 generation older Intel product when there was a viable current generation option available. ( Of late Apple has stayed on an older where Intel's new really hasn't offered much to jump "up" to. But that is actually part of the motivation to move off the platform. That isn't something Apple has demonstrated any desire to jump to for the Mac line up. )
In the Mac product line up, Apple is extremely likely going to take any CPU package cost reductions relative to Intel and apply them to something else. For example, if the SoC costs goes from $275 to $125 that Apple would apply that to a bigger SSD and/or better screen. That would leave the overall system bill of material costs the same , so the end user system price would stay the same.
Apple's $400/TB SSD pricing leaves their systems with relatively smaller capacities then the general competitive laptop/desktop market. The CPU package cost going down can largely be eaten up by just allocating a 512GB SSD starting point.
Similarly, Apple slaps large mark-up on the Intel CPU BTO upgrades they offer. Probably won't be a huge price drops there either.
Mac Mini. entry, standard configuration CPU i3-8100B ( $133 )
Intel® Core™ i3-8100B Processor (4M Cache, 3.60 GHz) quick reference guide including specifications, features, pricing, compatibility, design documentation, ordering codes, spec codes and more.
ark.intel.com
it has a $300 BTO upgrade to the i7-8700B ( using 8700 model link that has a price ) which is in the $329 zone.
Intel® Core™ i3-8100B Processor (4M Cache, 3.60 GHz) quick reference guide including specifications, features, pricing, compatibility, design documentation, ordering codes, spec codes and more.
ark.intel.com
So effectively Apple is giving only a $29 'credit' for turning in a $133 CPU. Apple is likely still going to have a relatively high binning+inventory mark up fee dropped on top of the Apple Silicon options.
Intel CPUs aren't 'dirt cheap' but a major contributing factor to the high end user cost of CPUs in Macs is Apple; not just Intel. That isn't going to disappear when it is an Apple SoC sitting there.
