How much could they roll their own for, few hundred thousand? Depends on timescale and starting point I suppose. But let's call it $1Million USD. That surely puts an upper bound on licensing the tech needed from NetApp to continue with ZFS. Perhaps they just think ZFS sucks?

Yeah, right. And they have been hanging to HFS+ for all this time because they knew it's a solid base for future development...

Sorry for the sarcasm, but I couldn't resist, but the very idea of Apple making a storage system like ZFS out of thin air is very... optimistic.

$1Million for a next-gen filesystem? The programmer wages for the testing phase will cost 10 times that.

Hans Reiser made a couple for no wages ... I guess that muddies the waters when considering the baseline for me.

Writing a file system isn't the hard part. Testing and verifying that it actually works under all kinds of strange scenarios and to make really really sure it won't corrupt your data, no matter what. That's the hard (and expensive) part. I seem to recall reiserFS being plagued with a number of bugs that only showed in uncommon corner cases that trivial testing wouldn't find.

I wouldn't expect them to use ZFS. It would be a really messed up court case when NetApps licensed the patents so Apple could use ZFS which NetApps was suing Sun / Oracle for a patent violation (head hurts). I would expect they would do a license to cover their own implementation of a file system.