Personally, I'm thinking of building a FreeNAS for photo storage / media, but unfortunately I've only got a four-drive array SuperMicro rack server (spare one I have from decomissioning a business).
Other things I'm interested in is perhaps hosting a few gaming servers and such for friends/family (Minecraft, etc.)
Hard to find uses for it other than offline-lowpower-media-storage.
I look at it as a modern version of the boxes full of pictures and slides my parents and grandparents kept in their basement for decades and never looked at.
My experience with the FreeNAS people was "build a second nas", but that always struck me as stupid for a home setup.
I've got rclone set up to encrypt and upload everything to ACD. There's a section at the bottom of the article that goes into some depth on this and some other backup strategies I've tried in the past (including CrashPlan, Backblaze, and Zoolz, all of which are awful). Check http://jro.io/nas#rclone . I never considered building a second NAS, it does seem pretty stupid, even for an enterprise setup. The whole idea is to get the data off-site.
As a side note, some of the so-called "FreeNAS people" can tend to blindly parrot a given general guideline without really understanding the reasoning behind it or why it might be perfectly valid in certain situations to disregard it. For instance, ask them about bhyve and I promise you'll get at least one response along the lines of "bhyve isn't officially supported in FreeNAS so you shouldn't use it under any circumstances, period."
If you're able to tag stuff you know you want to keep and it's a smaller set you could look in to something like Backblaze B2 (previously a featured story on HN); the storage costs are relatively moderate, but restoration from it will cost you.
I haven't yet heard of any solution along the lines of "Rent a (large) NAS for a month" for those times that you're upgrading your array and need to switch filesystem formats. Having that option would make the juggling much easier and safer. Looking at the S3 storage and bandwidth costs I imagine there is actually a market to be served by such a product.
Maybe renting one of those higher end tape drives makes sense... but I can't get over the idea that even renting a stack of hard disks would be cheaper and more effective at this scale.
PS: Make sure you encrypt all of the data going in to the temporary storage; those aren't your disks.
My home nas is small enough where I can reliably backup to some USB external drives and store in a drawer offsite. According to FreeNAS, that's a horrible solution because USB is too error prone and moving disks shortens their life, and blah blah blah, and so USB backup is explicitly a WILLNOTFIX, and a sign that the requestor is stupid, as opposed to knowing full well what the risks are, and is satisfied with them. The horrible FreeNAS community, and the lack of this feature was why I adopted OpenMediaVault. (I highly recommend OMV.)
I guess I could always upload TARs to Glacier. That might be a legitimate solution.
Think pretty much the only viable solution for this for home users is to have a 'peering agreement' with a trusted friend where you each colo the others machine at your home.. however this can be tricky because you're sticking all of your sensitive stuff in someone elses house and trading some level of full network acess to each other - though I suppose trading access to some kind of encrypted rsync-like dumps or similar might work without some of those risks being too high