Just got an email:
Stern Pinball's website has been updated with a few items on our support page. You can download the SPIKE Electronics System schematics and supporting documents on our main support page. In addition, we have added an option for updating code that utilize the SPIKE system. This option enables owners to create SD cards without assistance from dealers, distributors, or technical staff. Learn more about this time-saving option.
Not every board is there, but it’s a start.