Update: I spent most of my free time this weekend testing various coolers with the 3950x inside the S402. The only cooler that will work well enough to keep the thing from thermally throttling is the Enermax Aquafusion 120. When I tried running Prime95 on my C7Al, the system shut itself down due to thermal limits.
Once I figured out that none of the air coolers I used would suffice in keeping the 3950x cooled, I turned on Eco-mode and began testing. I haven't yet looked through the results but I've tested with the C7Cu, Thermalright AXP-100 full copper, and the ID Cooling IS-60. All the rest of my AM4 coolers will not work in the Asus X570 ITX board as the rear io cover and the m.2 stack interfere. Plus, I'm betting they cause a massive hot box for the CPU cooler. Edit to add that I also don't understand why the pump PWM interface cannot be configured as a fan PWM connector. Asus won't let you adjust the fan curve for that interface, it keeps it at 100% constantly so now I have to buy some more 4-pin splitter cables to feed my 3 chassis fans from one interface.
I'm probably going to have to acquire both an X470 ITX board as well as a 9-series CPU again so I can test the thermals on the rest of my coolers.
I'll try to get the results in graph form tonight and post them here but I'm going to be quite busy so it may take me a day or two.
Update #2: I just ordered 100+ 22mm push buttons. I'm going to have to solder the power and LED connectors onto each one but they are on their way. I also ordered a sample of a custom shipping box that will be just a little bit larger than the S402 so I can wrap it in 1/8" foam sheet and tape it up. No custom foam end caps or need to design something more complex.
Update #3: After installing the Enermax Aquafusion 120mm, I noticed that I need to add a zip tie mount to the PSU mounting bracket so that the hoses can be held down without pushing against the vented panel. Those will be added to the design for production. Because I had to use an SFF GPU, I installed my Vega 56 Nano and managed to also mount a slim 120mm fan behind it to extract air. I haven't tested yet to see what difference this makes but I'm hoping to get a picture soon of the setup I'm currently running because I think some people would be interested.
Only picture I have of the Enermax Aquafusion installed.
Things to do:
1. Order rear reset buttons and wires. Get wires for power buttons as well.
2. Test and order new PSU cables (will have to wait for next prototype).
3. Order USB front panel parts.
4. Generate a BOM for shipping so I can order all the various hardware (screws, etc.).
5. Set a deadline for possibly acquiring a new source for the PCIe cables. I've already identified compatible units and gotten prices but they are more expensive than my supplier.