I think I've just about finished rev B of the PCB - the main changes I've made are:

1. I routed a couple of the CP2110 GPIO outputs to the LPC824 reset and ISP entry pins so the ROM bootloader can be entered without the user pressing a button
2. I added an I2C EEPROM, which can be used for data logging and it's contents can be dumped over the USB-UART bridge

I was originally planning on including some sensors on board for a sort of all-in-one "IoT" platform, but I think it's more important to keep the cost down. The EEPROM is a fairly inexpensive part, and I think it's worth the $0.20 or so to add data logging as a core functionality.

I've pushed the latest changes to Github.