[willrandship] sent in a conversation from Reddit discussing the programming ports inside the Steam controller and their potential for hacking. From the posts and the pictures it seems the radio/SoC and the MCU can be programmed on the board, or at least they both have JTAG headers. The JTAG headers are in the form of “Tag-Connect” pads on the board so it will require the dedicated cable or soldering some hardware to the board temporarily.
From the pictures we can see a NXP LPC11U37F ARM Cortex-M0 and a Nordic nRF51822 ARM Cortex-M0 SoC with integrated Bluetooth low energy. There are only a limited number of Steam Controllers in the wild at this time so we don’t expect much in the way of hacking them thus far. There is a Steam Controller hackaday.io project just started for anyone who would like to contribute to the Steam Controller hacking.