The O3X project lead has joked about porting ZFS to Windows after he finished the Mac OS X port. That is the only discussion of porting it to Windows thus far,

The O3X project lead has joked about porting ZFS to Windows after he finished the Mac OS X port. That is the only discussion of porting it to Windows thus far, although there was one guy who tried reimplementing it as a userspace filesystem on Windows, but that did not get far.