This lead me to designing Revision 1.1 while flying on a plane a few weeks ago, and submitting it for fabrication.
I received the board this week, and after soldering the components to the board, I found only one issue this time. The LED headers were connected to a constant 5V power source, and the other pin was connected to the output from the I2C controller. This means that when that output was active, both pins would be getting 5V, which obviously wouldn't work. While this is actually a major flaw and killed functionality, I managed to cut the trace and run a wire connecting it back to ground, which has worked well so far.
Beyond that issue, this board works great and I am pleased with it. Having a solid prototype is helping me see ideas which I may want to expand on and stress test the overall design some more.
Looking to the future, I hope to build a unit containing the ATmega32U4 and the components I used on the shield on one board instead of using an Arduino development platform like the Leonardo. As well as a more integrated unit, I am also looking into adding the components for networking to allow a web interface to the hardware. With this, I am hoping to switch cameras from a smartphone, while still operating the tally interface
I also hope to integrate "broadcast" buttons, which would would find on a much more costly video switcher and contain LEDs under the keycap so you can see the status of the shot without looking at the software.
I am always looking for feedback as to what people might want to see in a device like this, and I know I'm certainly not done working on it. Please leave me any features you think would be cool or what you in general!