The high-end 24" iMac now has 2 extra USB-Cs that are USB 3 only, so it seems like Apple are quite prepared to have non-TB USB-C ports where needs must (whether it is because USB-A connectors are too deep, as on the iMac, or that there aren't enough TB controllers, like on the 12" MacBook).
USB-C is much smaller. It was design more so as an alternative to Lightining than a replacement for Type-A.
www.anandtech.com
Type A isn't the legacy connector that plays in the small device space. There is also mini and micro.
(from article link above. )
".. First, the mini connectors were introduced, which, at approximately 3 mm x 7 mm, were significantly smaller than the original connector, .... The smaller size did allow USB to be used on a much different class of device than the original connector, with widespread adoption of the mini connectors on everything from digital cameras to Harmony remotes to PDAs of the day. .."
Pragmatically Apple has turned the iMac 24" into a 24" iPad on a pedestal. Type A is out for the same reason it is out on cameras , phones, "thin slate" tablet, etc.
Apple had a dogma (since the edge thinning) that all iMac ports go into the back. That dogma ran into the even higher priority dogma on "even thinner , is even better". The Headphone jack and Ethernet jack moved too. That wasn't M1's Thunderbolt/USB internal implementation related. That was 100% the "thinnest" dogma.
Another substantive problem with the "these were suppose to be TB ports" is that these ports are imlemented in a substantively different fashion.
In the iFixit teardown they give Apple some positive "repairability points" for the USB-C (only) ports. Step 9 of the teardown.
Is the new M1 iMac just a silly-sized M1 iPad, a detached-keyboard M1 MacBook, an M1 Mac Mini stretched out like pizza dough? We’ll only know by...
www.ifixit.com
The ports are on a separate board so if a user "burns out" the USB port the repair is straightforward. This is a draughtboard swap out and it is not a whole motherboard swap out.
Speaking of the motherboard..... The "thin" dogma has constrained the logic board to be the same approximate size of the chin. As much as folks complain about the chin, its size on modern "small" screen iMacs is not that big.
If Apple attaches two more RAM stacks and makes the die used 40-120% bigge rto create a bigger SoC, where do all the other chips around the M1 here go ? The "X" in the name being used here is primarily to denote "bigger die and substantailly more stuff". If the iMac 24 still had an historically sized motherboard that would about zero problem to take a bigger package. ( the board had space for a CPU + RAM DIMMs + GPU + VRAM.). Apple threw
all of that away and painted themselves into a corner with a "chin size only" logic board.
[ the back of this logic board is pragmatically fully populated also. So "move some stuff on top to the bottom" isn't really an option either. ]
As a technological miniaturization exercise this is all pretty impressive. If look at an iMac motherboard from 4-5 years ago and look at this, it is truely a major leap. However, it is a dual edged leap. SoC size is going to be limited. RAM capacity size is going to be limited. Storage capacity size is going to be limited. If still had the old logic board area available all of those could be moved up an order of magnitude from what Apple has constrained themselves to here.
There is certainly enough here to be a "good enough" desktop system for a wide range of people. It can fill the original classic iMac mission. Moore's Law density improvements should allow them to put bigger caches , more specialized processors into the SoC. Also more capacity into the RAM stack and NAND stack chips.
The two fans here aren't really indicative of enabling a larger package (and TDP). It is much more likely what Apple is trying to do is keep the heat away from the LCD screen panel. The XDR monitor has fans to do the same thing with a lower board power consumption issue. If there aren't air movement across the board the heat from the board will rise straight up. Stright up from the logic board is the panel. You have now put an "Easy bake oven" under a LC panel... probably should have fans to get that heat out of there. the two fans also can spin slower than if just had one fan. So also an issue of keeping the iMac as quiet as possible. ( again because of the chin can't have a larger fan that spins slower, so forced into using smaller ones. Plus the speakers have be balanced so the a fan can't crowd the speakers out of the left ( or right) side. Everything has to be packed into this same single chin space. ).
Except the stolen schematics also suggested that there would be a SD card slot. Now, I might buy Apple trading a TB port for a HDMI port (esp. since losing the TB potentially frees up a display stream), but while SD would certainly be on my "nice to have" list I don't think it would make the cut if it really came down to "SD vs TB port #4". So I don't think the missing USB-C port is necessarily just a space thing - it will be down to only having 3 TB controllers. Or, assuming your point is right about needing simultaneous video on all ports for TB4 certification, just not being able to support 3 external displays...
Just 3 TB controllers would make sense if Apple is using full size Jade (10 CPU + 32 GPU ) dies to make Jade2C and Jade4C packages. the Jade2C would have 6 controllers with is already probably overkill ( but apple could reseerect the MP 2013 desing parameter. Probably to much hate from the same critics of the MP 2013 the last time). Jade4C would have gross overkill of 12 but that is incrementally better than a gross overkill of 16 .
Or since to get a close packed dies where the 4 corners meet layout , they'd need two "mirror' dies.
[T][P]
[P][T]
The lower right corner of the upper T would match the upper left coner of lower T when rotated 180 degrees. The lower left corner of P would match the right upper corner of lower P when rotated 180 degrees. The distance between those dies is minimized at that
One could drop the TB controller for PCI-e controllers in addition to adjusting the layout in mirror image. Would cost incrementally more but save space.
If they could make the "extra' TB pins outs from the SoC multiple functional those could be a could of x8 and x4 PCI-e v4 outputs in an optional configuration. Not going to make the dGPU add-in-card folks happy but there are range of storage, video out , audio , etc cards that would happy with a couple of x8's and x4's.
The x1 PCI-e v4 links are decent for an SD-Card. This new discrete solution only needs x1 or x2 PCI-e v3 worth of bandwidth. ( with v4 a future version wouldn't need x2 to get to "full speed". )
www.anandtech.com
Similar issue with E cores. Jade having 8 P and 2 E looks "funny" . but if multiple by four 16 p and 8 E looks pretty reasonable. The single building block looks like it has "too few", but once you multiple by 2 and 4 you get to plenty.
Maybe they are genuine Apple docs (or at least the "originals" were - most of the news stories seem to be rather garbled second-hand accounts backed up by bogus 3D renders...) but that doesn't guarantee that they are up-to-date schematics of actual machines in the pipeline for production. They could be old, obsolete, prototypes, contingency plans for M1-based 14/16" MBPs if the M1X fails...
"bogus 3D renders" or 3D renders as replacement for Apple take down requests ?