Ok, first off I can't believe that we are still having this discussion, and that Plesk 10.1 _still_ doesn't have native IPv6 support in addition to IPv4 support.
This feature has been promised since version 8, and I have had cast iron assurances from senior members of Parallel's staff that it WILL be in the next version, since version 9, 9.5, 10 and then 10.1
We absolutely have to have IPv6 support this year ... in fact, we needed it 2 years ago, and we asked for it originally nearly 5 years ago
Dual stack is essential. The ability to have multiple IP addresses for a single domain is also key.
The ability to assign a netmask onto the interface (/32, /48 or whatever in IPv6 terms and a /24, /23 or whatever in IPv4 parlance as a single instruction to Plesk).
We might host 2,000 domains on a server, and a lot of those need dedicated IP addresses for SSL or whatever.
We need IPv6 support in all the tools, PBA for DNS management is an obvious one ... as is the ability to have IPv6 and IPv4 native name servers, ftp servers, mail servers and so on.
Currently we have to kludge Plesk and PBA to support IPv6 and it sucks.
Hosting companies will need time to get used to running IPv6 under Plesk, and with the current exhaustion rate of addresses, they're going to find they have no v4 address space left and they won't have enough experience of v6 / all the bugs worked out of Plesk's v6 support before they find they're hosting thousands of sites on v6
We've been running IPv6 networks here at Fido for over 10 years ... Time really is running out for Plesk and IPv4, whether Sergei and his crew believe it or not!
Jon Morby
FidoNet / Fido LLC
www.fido.net