"5 years support or until the lawyers wade in over licensing.
Not sure if open source fights like this are a sign of approaching maturity or senility."
I think that concerns over the implications of the Common Development and Distribution License that applies to OpenZFS are valid. That said, three of the four informed legal opinions I have seen so far support Canonical's position with the only dissenting opinion coming from the Software Freedom Conservancy (no surprise there then). I also strongly suspect that behind the scenes Canonical will have explored the legal position in depth so that they are in a strong and defensible position.