After a week of waiting for parts and a late night of tinkering, I have a Raspberry Pi 2B passing traffic over WiFi through an ESP8266 that thinks it's an ESP8089. My first attempt is ugly: the wiring is fragile, it needs to be power cycled if the driver is unloaded, and the connection is ~1.5Mbits at best, and my failure to keep the perfboard out from under the antenna limits the range greatly.

An FTDI cable (seen in the pics above) is wired to the ESP's UART to monitor the SDIO boot process and (as I discovered) get state info from the firmware. Other than that the only interfaces I used during testing were a USB keyboard and HDMI video.

Todo: look into what SDIO mode we're running in, scope the bus to rule out SI problems, get the modified driver in github, push a small change to the rpi kernel 4.2 branch, document this mess, test on the armv6 build when my Pi A+ gets here (closest to a Zero till the mad rush is over)