ofcourse linksys and dd-wrt are not really comparable.
I've just setup a other customer from the bounty forum with a working IPv6 setup. With a gif tunnel or static addressing on the wan it does work with v6. With recent fixes I've made it should be safe to run either v4 or v6 on the same interface. I fixed the issue that made it drop it's v4 default route.
If you do not mind giving me remote access to that install to develop working ipv6 support then I'd love to get that working. It is probably the most significant building block for IPv6 deployment on cable internet networks.
And there are a lot of those.
If you have questions, feel free to climb into the email to firstname.lastname@example.org and we'll see what we can arrange.
I've just made some fixes to filter.inc for dhcpd, the webui listen port on the v6 address and a DNS rebinding attack fix.
I've also added v6 network support for the ipsec phase2 page. Maybe I can fix the phase1 too.