I uploaded a kernel module for kernel version 4.4.48+, which corresponds to 2017-02-16 raspbian.
On another note, with the release of the Pi Zero W, this project is obsolete.
Or is it really? After thinking about it, I realized it could still be useful for a multi-radio mesh node. So, I'll make some modifications so it will work better in that role.
The only thing I'll have to do is redesign the PCB. Basically I'll flip the ESP module over, and let it hang over the GPIO edge of the Zero a bit. It'll make the assembly a little bit larger, but improve signal strength greatly, both for the ESP radio and the one built into the Zero W.
Using this, and a USB WiFi adapter, you could build a three-radio mesh node without using a USB hub!