Is IPv6 support planned/in the works?

In OpenVPN releases older than 2.2-RC2 there's limited support for IPv6. Point-to-point IPv6 tunnels are supported on OSes which have IPv6 TUN driver support (this includes Linux and the BSDs). IPv6 over TAP is always supported as is any other protocol which can run over Ethernet. When OpenVPN 2.0 is run in server mode, IPv6 is only supported in TAP mode, not TUN mode. The VPN carrier connection must use IPv4 endpoints.

In OpenVPN 2.2-RC2 IPv6 in TUN mode was implemented for the Windows TAP driver.

Full IPv6 support is already available in "allmerged" branch in Git, and will be included in OpenVPN 2.3.