First up for the HID Linux 3.16 pull is an RMI driver, which is for supporting Synaptics RMI4 devices over USB or I2C. The RMI driver right now uses its own RMI4 implementation but will ultimately become a transport driver for the RMI4 library once it's been merged upstream. This driver was developed by Synaptics along with Red Hat and other independent kernel contributors.
The other noteworthy change for the input driver updates in Linux 3.16 is a clean-up of the Sony driver with improved support for the Sixaxis and DualShock 4 controller -- it was just with Linux 3.15 that came DualShock 4 controller support.
There's also other various bug-fixes and new device ID additions with the 3.16 HID pull. More information is available from the kernel pull request.