Jumping in here...

I'm replacing my 2009-era MacPro with a brand new one, and of course there's nowhere inside for hard drives. After staring at all these issues, I decided to go with the LaCie 5big. There are two variants: Thunderbolt and NAS. I went with the Thunderbolt model, which just exports five JBOD disks and leaves it to your host for RAID or whatnot. This would be perfect if only Apple supported ZFS, but they don't. Likewise, it would be great if you could buy the enclosure without disks, but they only sell the NAS variant diskless.

Anyway, I've got just shy of 2TB on my primary partition, today, so I'm going to do two different RAID stripes. 3x2TB for primary storage, and 2x2TB for Time Machine, yielding something of a sort of RAID 1+0 setup, with plenty of room for me to grow my disk usage before I have capacity issues again.

(Yes, you normally want the Time Machine partition to be bigger than what it's backing up, but I figure I want the primary partition to get the extra speedup of the third disk in the stripe. If/when 4TB becomes inadequate for the TimeMachine side, I can replace the 2TB drives with something bigger.)

What does this mean for an Intel NUC? It seems some of them have Thunderbolt and some don't. If you've got the Thunderbolt variant, you could plug that LaCie box in, run FreeBSD / FreeNAS or whatever else, and you've got five disks upon which to run ZFS. That's pretty attractive.

(For the lack of GigE, you could daisy-chain a Thunderbolt-GigE adapter -- $29 from Apple.)