It's been added to the requested list. Not sure though.
Even though Browsers are currently the main thing using IPv6 along with the connection protocols, I haven't seen or heard of many games and or game consoles using IPv6 as of yet. Not even sure if the newer gen consoles coming out are support it yet.
This could be one reason why D-Link might have left it out and didn't see a need for a gaming router with gaming applications that are not set up for IPv6 currently. This is a gaming router mind you. Ya, I guess it would be nice for all non-gaming applications that support IPv6 to be able to have access in this router as it's becoming more prominent as time goes on. My ISP still hasn't even considered it.