Here's the current status of the PCB for the new OneHand design. I've changed this version to use a 1.5u cap on the two larger keys as this allows a more compact PCB, and removes the headache of sourcing stabilizers. I may revert to the 2u keys if needed in the future.
The design uses a 48-pin STM32F072 Microcontroller and has the option of adding an nRF51822-04 Bluetooth BLE module ($4 off EBay) and a Lithium Ion Battery. I've wired all the signals from the BLE module to the STM32, and therefore it should be able to in-circuit reprogram the BLE module with a little effort. There are a couple of routing improvements I've just spotted, but all the components are placed and routed.
The expectation is that you can build a USB only one handed keyboard by not populating some of the components, and also create an I2C second secondary keyboard, which does not require the USB or power supply components to be installed, to speed up build and reduce cost. Parts cost of the design (less switches & caps) is around $25-30, with the second hand being around $10-15.
There's a charging LED in the top middle switch, and the option of either 3 LEDs at the bottom separate from the switches, 3 LEDs embedded in the bottom row of the keyboard, or an RGB LED in the center bottom key using a Gateron switch body.
I'm hoping the BLE module will allow a HID over GATT link to make the keyboard wireless as either a single or two handed design, but I don't know how well this will work. I have a fallback of adding a separate BLE module between the two keyboards to provide the link.
I've also been working on a 3D printed tray which will hold the PCB and if needed the battery.