The team who are working on the IPv6 issue have a meeting coming up. I have voiced your questions and they will be wriiting the answers to your questions together at the meeting.
From what I can tell, pretty much none of the Draytek's support IPv6. I had the Vigor 2600 Plus and that doesn't support IPv6 (I think it's end of life too).
I also have (and currently use) a newer 2820 and that too doesn't support IPv6. If you look at their forums, you can see people almost pleading Draytek to add IPv6 support via a firmware update but nothing's come out so far.