Good news. Got this working on Seirra with Poseidon Z using https://github.com/thefloweringash/iousbhiddriver-descriptor-override/issues/33 Bad news. Characters stop working after about 50 key presses. Can install with https://thefloweringash.com/iousbhiddriver-descriptor-override/downloads/IOUSBHIDDriverDescriptorOverride-2016-11-13-cfa5838.pkg Note you will need to enter recovery mode and disable SIP. Instructions -FWIW, to anyone who's thinking of disabling SIP fix the kext signing issue, it's possible to only disable the kext signature checking and leave all the other protections enabled.
All you need to do is in recovery mode after disabling SIP with csrutil disable, enable it again but without kext signing enable with csrutil enable --without kext. The util will give you a warning about this feature possibly being unsupported in future versions, so be forewarned this might be a bad idea.