@doki
Are you familiar with ImageBuilder?
In short, all you need is a UCI file adding into your image to switch on the wifi.
The files folder is where you put files to be included in your image, create it if you need to ie imagebuilder/files
Then in the files folder of imagebuilder create etc/uci-defaults/customwifi
containing the following:
#!/bin/sh
uci set wireless.@wifi-device[0].disabled=0
uci commit wireless
exit 0