Word on the street is that Sun is exploring the option of going GPL at the CEO level. They have been chatting with customer council(s) about whether they should do this.
The answer is simple: Do it. Do it now.
ZFS has inspired many. There are a number of up and coming new filesystem and large scale storage solutions being developed under the GPL like Btrfs, Tux3, and Ceph that all have similar characteristics to ZFS.
If you don’t GPL it now, you’ll lose the opportunity to make the kind of difference you are trying to make.