The most interesting (and tragic) part of this, to me, is not that ZFS is being rebased from Illumos (open source Solaris) to ZFS on Linux:

... it's that Solaris is effectively finished as an OS. It's not even its own upstream anymore for arguably the greatest modern contribution to any OS.

This is tragic, and needless. Oracle effectively shot itself in its own foot with the pointless and deliberate choice of licenses, the on-again, off-again open sourcing of Solaris, and the complete lack of commitment. Solaris had a real shot of remaining a fine alternative UNIX operating system, at least for the server side of things, but now this shot is gone.

They killed Solaris like they killed Java.