The new boards are built and a very pretty blue they are.
I mounted one up on the greenbot and it works as designed.
I made up a test jig and an arduino sketch to wiggle all the pins and watch them from another PCF8574.
I did run into some timing issues reading from the jig, but those went away when I turned off the Serial.println commentary. I'm thinking there is some weird interaction between the Wire and Serial libraries.
Pictures in the gallery