To provide LuCI support for IPv6-in-IPv4, navigate to LuCI → System → Software and install the packages 6in4 and luci-proto-ipv6. Then navigate to LuCI → System → Startup → Initscripts and click to network → Restart to be able to utilize the new protocol.
OpenWrt is fully capable of handling and routing IPv6 traffic. Many ISPs offer native IPv6, but if yours doesn't, here's a quick setup guide for experimenting with IPv6 (and getting used to the peculiar address format).
The procedure below creates a 6in4 tunnel on the WAN6 interface of your router. This automatically wraps (encapsulates) all IPv6 packets inside IPv4 packets, and sends them to a designated tunnel broker server that unwraps them, and forwards them to the destination IPv6 host. Packets from those IPv6 hosts go to the tunnel broker server, where they're wrapped in an IPv4 packet and sent back to your router, which then unwraps them for for use on your local network.
Before you can configure your router, you must set up a free account at the Hurricane Electric Free IPv6 Tunnel Broker site, then create up a Regular Tunnel. Be sure to click Assign /48 for the “Routed /48” field. The Hurricane Electric Tunnel Details page (image below) shows the details of your tunnel.
To complete the OpenWrt configuration, open the router's Network → Interfaces page in a separate tab or window, find the WAN6 interface, and click Edit:
You'll see the WAN6 Common Configuration page (image below). Copy the values from the Tunnel Details page to the corresponding field of the WAN6 Common Configuration page:
At this point, your computer should have direct IPv6 connectivity with the rest of the Internet.
(You may need to restart the router, or disable and re-enable the network interface of your computer before the 6in4 addressing works.) To test, type