IPv6 SEO implecations?

[Wil Schultz <wschultz () bsdboy com>]

I'm attempting to find out information on the SEO implications of testing ipv6 out.

A couple of concerns that come to mind are:

1) www.domain.com and ipv6.domain.com are serving the exact same content. 
Typical SEO standards are to only serve good content from a single domain so information isn't watered down and so that 
the larger search engines won't penalize. So a big concern is having search results take a hit because content is 
duplicated through two different domains, even though one domain is ipv4 only and the other is ipv6 only.

2) Not running ipv6 natively, or using 6to4. 
This (potentially) increases hop count and will put content on a slower GRE tunnel and add some additional time for 
page load times. 

3) ??? Any others that I haven't thought of ???

So basically I'd love to set up some sites for ipv6.domain.com via 6to4 as a phase one, and at some point in the near 
future implement ipv6 natively inside the datacenter, but I'm somewhat concerned about damaging SEO reputation in the 
process. 

Thoughts?

-wil