Any other computer I could simply replace the motherboard with several other compatible motherboards, no soldering or donor board needed.
Can you just fix an F1 engine with a wrench?
In fact the current Gen is bigger than the trashcan ones by quite a bit (although IIRC the trash can Macs had user replaceable SSDs and GPUs)
I totally missed that they released a new Apple Silicon Mac Pro. Turns out it has PCIe slots.