Allowing guest port forwarding from vhost_addr/vnameserver_addr

Is there a fundamental reason why guest forwardings with host/nameserver addresses as the guest address are not allowed?

Sometimes it can be very convenient to rebind a port on the host address to something else, e.g. if the guest is hardcoded to access http://<dhcp next-server>:80 and we'd like to redirect that to a non-privileged port (since not having root privileges on the host is pretty much the entire point of using something like slirp).