Interestingly enough, IPv6 just started working natively after updating my Time Capsule tonight. I'm in the Cox Omaha market for reference. And disclaimer: this makes no sense to me but I assure you it happened just as I say.
After the update, I switched from Link-Local to Automatic+Native and unlike before when I would get neither IPv4 nor IPv6 traffic, I retained IPv4 traffic (still no IPv6). A little progress at least, right? Then, just for curiosity's sake, I switched to Automatic+Tunnel and I suddenly began routing IPv6! The Time Capsule started blinking and complained about an IPv6 relay error. BUT, I still had Internet traffic and I scored 14/20 on IPv6-test.com. Very weird. Obviously, I wanted the indicator light to stop blinking so I changed it back to Automatic+Native. Then, it got even weirder. The Time Capsule isn't complaining, I still have IPv4 traffic but now I ALSO have IPv6 traffic with a score of 16/20! Try explaining that.