A lot of our processors don't have printer interfaces! We do sometimes blink an LED or wiggle a test-point port pin to trace realtime program execution.
This one has 13 ARM processors, one manager and 12 of them in electrically isolated i/o channels.
We're having all the ARMs programmed by a distributor with boot loaders in their on-chip flash. We plug one serial flash chip into a socket for all the runtime firmware. At powerup, the main CPU boots its runtime code into RAM from the serial flash and then loads all 12 slave processors with their actual runtime code, too.
We have JTAG socket footprints on all 13 cpu's, but we don't solder them in unless we need them.
All pretty far away from plugging a graphics card into some mobo game machine.
John