When will pFSense 2.2 be out? And will it still correspond to FBSD8.3, or 9? Also, in FBSD9, there is an IPv6-only option that can be installed, so that developers can test whether their applications really work w/ IPv6. Would any version of pFSense have that, just in case anybody wanted an IPv6 only router and firewall but not any IPv4?
2.2 will be a bit far out yet, not sure. We'll be targeting FreeBSD 9.1 or so for that. We wanted to be on 9.x for pfSense 2.1 but we had far too many issues and backed down to 8.3 which was much easier to adapt. Since 2.0 took so long to get out, we decided to try and do more frequent releases, about every 6 months or so. That's slipped a bit, but we have had some security releases for 2.0.x since 2.0 came out (2.0.2 is coming out in 1-2 weeks) so it hasn't looked like such a long gap as we had between 1.2.3 and 2.0. Using that logic, I'd expect 2.2 sometime before or near the end of the year. It depends on what all we decide to add for it.
If you want IPv6 only, you can do that on pfSense 2.1 now. We have a developer that has a v6-only circuit in .nl and pfSense 2.1 is routing it fine, that's how we've debugged some of the issues. If you want v6 only, you can configure only v6 IP's on interfaces (and set v4 to 'none') or block v4 in firewall rules. What FreeBSD 9 does better there is that you can completely remove it at the OS level as well for things like localhost, which isn't quite so important in a routing role as it would be for a client platform.
Also, would pFSense come w/ a built in DHCP6 server?
Sure, it does Router Advertisements as well as DHCPv6, and they can be configured to work complimentary to each other. Of course since it's wrapped in a GUI there may be certain scenarios you can't do (yet) with DHCPv6 but most things that most people want to do are possible.