We are never going to be able to connect to the host loopback.
According to this stack overflow answer http://stackoverflow.com/questions/87442/virtual-network-interface-in-mac-os-x you can add aliases to loopback, which you might be able to use to give yourself a fixed address with eg ifconfig lo0 alias 172.16.123.1 - not tested this.
We currently cannot create an additional IP address due to some issues with OSX, and it is quite nice not having to interfere with the OSX network interfaces anyway, so we are less likely to break anything locally, or interfere with other software - even finding an IP address range that is unused can be difficult.