Having received another reply from Netvigator TechSupport here the follow up on my previous post.

Although their network quite obviously supports IPv6, as they operate the site http://ipv6.netvigator.com, they do not offer IPv6 to customers.
That is, I have to say, quite sad, as this shows that Netvigator apparently is not able to move along as technology develops.

If, as I somehow suspect, they just now started implementing IPv6 then this was really poor judgment, as testing could have been much earlier, in order to be ready to deploy IPv6 when it becomes necessary, which is now!

Yes, IPv6 has taken some time to become relevant, and I acknowledge the fact that it has been ignored by many over the last years. One big factor in this certainly was NAT, but with more and more devices being Internet-ready; not only computers, but also phones, TVs, ebook readers and vibrators; IP addresses in the IPv4 space have now run out, and we’re at a point where NAT just doesn’t help anymore.
Sure, you can run a bunch of servers on the same IP, but who would want their visitors to have to type in strange port numbers in order to visit their website?
IPv4, and with it NAT, has become incapable of keeping up with the exponential growth of the Internet, and now it’s time to switch on IPv6 for everybody. There was enough time to test. Big ISPs like Netvigator should have deployed a bunch of networking wizards long ago to implement and test in order to get their infrastructure IPv6 ready for the day where IPv4 just doesn’t cut it anymore.

As I will be moving back to Germany this summer I have today decided to contact my probable future ISP, T-Online, with the same question.
Does T-Online offer customers IPv6?

Thank you!
Dennis Wronka