Netflix has been developing in kernel and userland for this; if ZFS for content was a priority, they could make 0-copy sendfile work. Yes, it's not trivial at all. It will probably happen eventually, by someone who needs 0-copy and ZFS; or by ZFS people who want to support more use cases.

Yet does not suggest any sort of impending completion.

We haven't been to the center of the galaxy yet.

We haven't achieved immortality yet.

Both are valid sentences without any fixed timeline, and in the case of the first, a date that is hundreds of thousands of years in the future at soonest.

"yet" just means "up until this time" (in conext, sometimes it means "by the time you're talking about" - e.g. I'm scheduled on-call on the 13th, but i won't be back from my PTO yet).