Two issues you are completely ignoring are "barrier to entry" and "PITA factor". I can control a bunch of LPT-attached LEDs with two lines of shell script or b

Two issues you are completely ignoring are "barrier to entry" and "PITA factor". I can control a bunch of LPT-attached LEDs with two lines of shell script or bitbang SPI/1W/whatever with a screenful of C. No reason to design one-off PCBs and make those external devices "smarter" than they need to be.