Are there any plans to add IPv6 support to OpenSprinkler? This would make it unnecessary to implement port forwarding, which can be problematic if your internet provider changes your IP address when your DHCP subscription expires. ISPs will often change your IPv4 address, but should never modify your IPv6 assignment.
For microcontroller-based OpenSprinkler, I did some Googling, and found that the current Ethernet library (EtherCard) does not support IPv6, but another library (UIPEthernet) does. We do have plan to change the code over to use UIPEthernet, and at that point IPv6 will be possible.
For OSPi, this is just a question of whether RPi supports IPv6, which I assume it must be able to.