The potential risk to ZFS created by the shift in its userbase

The obvious conclusion we can draw from FreeBSD ZFS’s shift to being based on ZFS on Linux is that the center of gravity of open source ZFS development has shifted to ZFS on Linux. Unfortunately, I think that this shift creates risk due to a consequence of ZFS on Linux not being GPL-compatible, which is that working with the Linux kernel’s ever-changing API could become sufficiently much of a problem that ZFS on Linux development could end up coming to a halt. If ZFS as a whole is increasingly dependent on ZFS on Linux development and ZFS on Linux development is partly a hostage to the not particularly friendly views of Linux kernel developers, a problem there affects not just ZFS on Linux but everyone.

Source: utcc.utoronto.ca