>but the goal should be to have the raspberry pi wifi driver expose
>a compatible interface to aux/wpa. 

I know your way, and agree with you.

I'm now trying to have a working model for rpi3 wifi network.

I first tried to port it into 64bit /sys/src/9/bcm64 with your port/wifi.c.
It is very complicated, one is related to 32bit/64bit difference where
I have to know the hardware knowledge of rpi3 completely.
To combine the Richard's driver with port/wifi.c is based on above assumption
that I know rpi3 hardware deeply, such as gpio etc...
It's not possible to me now, so I abandoned this course temporally.

A more combenient course to me is take the Richard's codes 
with small changes as possible as, and have a working model at first.
After make it done, I'll return to the course you suggested.
This is my roadmap for making rpi3 wifi network here.

Kenji

PS. I can't find your new net.rc on 9front tree. I can find only the same
net.rc as my /sys/src/9/boot/net.rc.