With the SLOT Processor on a Backplane.
*MANY* Industrial computers used them and made it impossible to get outside parts and accessories... anywhere else.
SBCs have been around for ages. Many blade servers have many things soldered on. Processors and memory are just the latest ones.
Fewer options == cheaper to manufacture and support long-term.
Also, Processors being on a card is nothing new, PIII-Xeons in IBM servers and other big name providers had CPUs on cards that could be disabled and removed HOT or added and enabled HOT.
Its just a realization Intel pursued in the high end before and re-introducing it or gagging the industry with it again.