I think this is possible. OpenSprinkler uses Microchip’s ENC28J60 Ethernet controller, which is one of the lowest cost Ethernet controller. It does not have hardware Tcp/Ip stack, so the downside is that the stack has to be implemented in software. But with respect to IPv6, this is also the advantage: that is, it’s just a matter of changing the software to incorporate IPv6. I’ve seen a couple of online posts that discuss this. Google ‘ENC28J60 IPv6’ to see related posts.