In my current set up, my gateway address is different to my actual IP address (I have an internet facing IP, however my gateway is a separate address, like many other server set ups) - this is causing issues with the myPlex auto-discovery that cause a lot of extra work and network configuration to allow to work. This could very easily be solved if you had a 'manual' option on the myPlex discovery page within the PMS settings.
I'm not 100% sure why this isn't already a feature, but I am certain it would not take too long to implement
Not quite… If you look at [plex.tv/pms/resources.xml?includeHttps=1] you see all the Plex Server’s local IP addresses (including things that wouldn’t route, like iSCSI bindings) that come before the URL or the external IP address. This causes unnecessary delays on both local and remote access. Like other sorts of servers, I’d like to be able to define the IP bindings that’re used by the server and published in the resources.xml.
The feature of allowing the user to select a specific network interface is now available as from Plex Media Server version 1.13.5.5291 which was released to Plex Pass beta yesterday