IPv6

I realized I hadn't actually written a reply to this, only to other people's replies.

There's a couple of problems with doing this. First and foremost is one of principals. IPv6 was designed with the explicit goal of killing off NAT, bringing it forward in this way is counter productive. That being said there's a much bigger problem here. IPv4 addresses are 32-bits, IPv6 addresses are 4 times larger at 128-bits. There is simply no way to fit an IPv6 address in an IPv4 packet header, it's simply too big. There are ways to do v6 internal with v4 external but that's only possible because v4 addresses are so small and can easily be fit inside the v6 address header, what you're trying to accomplish just isn't possible from a technical standpoint alone. I would recommend either dual stacking your network, that is running both v4 and v6 at the same time, or if you wish to go single stack you can run pure v6 internally and use NAT64 to get access to v4 services however there are a few caveats with this setup you should be aware of if you want to go down that road.