I haven't even received the prototype board yet and I've already had that awful thought: "How could I make this better? ...Cooler?"

So, I've made revision 2. It's the same schematic layout as rev1, just arranged differently on the board. I'm familiar enough with kicad at this point to know how to modify footprints and remove pins, so I've got the teensy and the i2c expander sharing a footprint now. I also went ham on the angles:

I also thickened up the traces by 50% just in case, and just in general arranged everything much more cleanly. It's really starting to shape up.