I think they're just not happy with the specific way TRIM support was added, and want to add that feature but architected in a somewhat different way. There was

I think they're just not happy with the specific way TRIM support was added, and want to add that feature but architected in a somewhat different way. There was a thread on the illumos-zfs list in February 2013 where an alternate proposal w/ prototype patch was made (the thread also has some comments from the author of the FreeBSD version), but it doesn't seem to have been finished/merged.