See Ludovic Ronsin's answer belowLudovic Ronsin's answer above about using dtoverlay, a method added in January 2017.
This post seems to be talking about this. The answer talks about disabling the drivers by editing the file /etc/modprobe.d/raspi-blacklist.conf and adding:
blacklist brcmfmac blacklist brcmutil Alternatively, you could use crontab -e and add:
@reboot sudo ifdown wlan0 So that command runs at each boot.
Hope this helps, I'm still waiting for my Pi 3 to arrive.