RGB background light might seem unnecessary at first, but in context and with some thought it's a good indicator for things. To save pins I'm throwing an attiny13/45/85 on the board to let a BlinkM clone handle the RGB controlling.
On that I2C is also a PCF8574, an IO Expander that will scan the buttons for me.
There is a grove connector - basically almost a 2mm JST connector - that will allow me to add some sensors or another board that I'm working on for sound #T85SID - I2C sound thing
When it comes to power, I've wanted it all, meaning the board needs to be able to charge a LiPo with the help of an MCP73831 but also stay on when I plugin USB or remove it. For this I've integrated the TPS2113A, a power mux chip that does just that and keeps me from throwing in diodes at everything (that chip was also featured in a 3hours youtube live stream by David Watts - great watch!)
For connectivity I've copied from the known ESP breakout boards out there, that use the CH340G as a serial to USB converter and also a flip-flop circuit for pulling GPIO and RESET at the right time.