Google for PC/104 its exactly what you're looking for although its aimed at industrial control users (and unfortunately priced accordingly) Of course if you co

Google for PC/104 its exactly what you're looking for although its aimed at industrial control users (and unfortunately priced accordingly) Of course if you could guarantee a production run of 5 million then a contemporary PC/104 board could probably cost as little as a ras-pi. Note that there's PC/104 the concept and form factor, and another concept with the same name was a 104 pin header that was vaguely a PC/AT bus. After all, S-100 can do almost anything so an extra 4 pins shouldn't hurt anything LOL. Anyway my point is if you find references to the 80s era 286-AT level of performance bus, don't worry for a decade there's been stackable PCI equivalents and all that. Something to think about WRT "limited" PC/104 bus speed is its not like spec-ing gamer graphics cards... if the purpose of the bus is to connect a 4 kilosamples/sec 12 bit A/D converter, even something as slow as RS-232 would not be a limiting factor, for example.