Great and thanks for creating as an issue. It is inline with some of the solutions I have been reading in the caddy community over here
example.com {
@trusted remote_ip 10.1.1.0/24
@untrusted not remote_ip 10.1.1.0/24
root * /usr/local/www/html
file_server @trusted
file_server @untrusted {
index untrusted.html
}
}