Can I disable wifi on boot? System not booting That is, are there nvram boot-args to disable wifi or a startup key sequence that does?
Safe mode is said to PARTIALLY disable Wi-Fi on some Macs. 

I googled and couldn't find an answer. 

Haven't managed finding/searching the source code because that's hard to do from ths iPhone. My Mac is not booting normally... Even in safe mode. (Diagnostic running now. ) 
I'm getting an error about AWDL mode suspending and I recently enabled AirDrop and so I want to see if I can boot if I completely disable Wi-Fi.
I have a MacBook Pro (Retina, 15-inch, Early 2013) and tested the following on it.

With my Wi-Fi network adapter turned on and connected, I shutdown my MacBook Pro. (This was to ensure the change I was about to make did indeed disable my Wi-Fi network adapter when rebooted.)

With the MacBook Pro shutdown, I then started it in single-user mode.




  Start up in single-user mode or verbose mode
  
  Use these steps to start up your Mac in single-user mode or verbose
  mode:
  
  
  Shut down your Mac.
  Press the power button to start up your Mac.
  Immediately hold down the following keys:
  
  
  Hold down Command-S for single-user mode.
  Hold down Command-V for verbose mode.
  
  
  
  You've successfully entered single-user mode or verbose mode when you
  see white text appear on the screen.



If you can't enter single-user mode, see How to start up your Mac in single-user or verbose mode for additional details.




In single-user mode, run the following commands:

/sbin/fsck -fy
/sbin/mount -uw /


Once the filesystem has been checked and you've mounted the / volume as writable, use the following command to disable the Wi-Fi network service, which will turn off the power to the Wi-Fi network adapter when rebooted into normal mode.

networksetup -setnetworkserviceenabled Wi-Fi off


Now reboot using the reboot command, type reboot and press enter.

Once rebooted and in normal mode you can reenable the Wi-Fi network service, thus restoring power to the Wi-Fi network adapter, by doing the following.

In Terminal, use the following command:

networksetup -setnetworkserviceenabled Wi-Fi on


You'll be prompted for your password, as shown in the image below.



Type in your password and click the Modify Configuration button, or press enter.



Note: While in single-user mode, if your wireless network service is not named "Wi-Fi" then use the following command to determine what network services you have.

networksetup -listallnetworkservices


On my system, after using networksetup -setnetworkserviceenabled Wi-Fi off the output was:

An asterisk (*) denotes that a network service is disabled.
*Wi-Fi
Display Ethernet
USB Ethernet
Display FireWire
Bluetooth DUN
Thunderbolt Ethernet
Thunderbolt FireWire
iPhone USB
Bluetooth PAN


So, "Wi-Fi" was the right choice for me.



Note: I do not have FileVault enabled and if you do, you may have additional steps to take to access single-user mode.