Feature for full mac randomization in the welcome screen users can 
select if they choose so (not set as the default spoofing option.)
Something like these lines added to /usr/local/lib/tails-spoof-mac
oui=list of phone oui venders
nic=/usr/bin/tr -dc a-f0-9 </dev/urandom | /usr/bin/head -c 6 | /bin/sed 
's/../:&/2g'
spoof_full_mac() {
     local msg
     set +e
     msg="$(macchanger -m "$oui:nic" 2>&1)"
     ret="${?}"
     set -e
     if [ "${ret}" != 0 ]; then
         log "macchanger failed for NIC ${1}, returned ${ret} and said: 
${msg}"
         return 1
     fi
}
macchanger command for this feature would be
macchanger -m "$oui:nic"
phone oui vendors resources to form oui list:
https://standards.ieee.org/products-programs/regauth/
https://www.wireshark.org/download/automated/data/manuf
(look for these type of vendors)
Google
Huawei
Apple, Inc.
Samsung Electronics Co.,Ltd