I am sure I'm doing a bunch of things wrong, but so far the "Rules Check" features have been appeased.
Up to 8 of these boards will be able to ride the same i2c bus. (Up to 16 if you use the pcf8574a variant on half of them.) This one doesn't do a separate latching step, but maybe a later design will. Yes, I know I'm not putting in room for a real heat sink on each Q0-Q7 package, I don't need that much dissipation. I may add a power jack alternative to the +12V pins of the cable header. The M hookups are at the right pitch for a block of screw terminals, or they can be soldered directly.