Here are my thoughts and what I know (not affiliated, but actively looking for tons of cheap storage, so very interested in ACD)

This is the public world record for high you can go with ACD if all the planets align:
https://i.imgur.com/kiI4kmp.png (small screenshot) /
https://www.reddit.com/r/DataHoarder/comments/5s7q04/i_hit_a...

At the other end of the spectrum, I learned from some archivists a little while ago how someone hit some kind of impenetrable brick wall at only 100TB. I unfortunately don't know what their upload size/time ratio was like or if the data was encrypted.

Here are my thoughts.

Amazon are selling unlimited storage, and clearly have the capacity to actually support surprisingly deep file lockers, so they're making good on their promise and letting people just feed them files all day long.

But when you get to this level of scale, you have to seriously think carefully about what you're storing.

If it's encrypted, why is it encrypted? If it's PCI-DSS data, that shouldn't be on ACD, that's commercial usage. If it's surveillance footage, home environments don't generally create terabytes of footage as the months go by (unless the DVRs are garbage). Etc etc.

My point: it's generally hard to find a home/personal use to store data that must categorically be encrypted, so the only reason data will be encrypted is either a) paranoid types who want to keep their data to themselves or b) people who have something to hide. (a) are annoying, but (b) are a liability.

One thing I can imagine some types of people leaping at ACD for is storing encrypted tomes of porn, the kind that generates FBI visits and makes people go away. Considering that Amazon is making good on their offer to actually provide tons and tons of space for ~$60/yr, the scale of data that is being stored becomes a liability if it's encrypted, because you don't know if it's bad material.

The reason for this is that, if the keys to the encrypted tome(s) get out, and a lot of content is discovered in one place, it's possible Amazon could get caught in the ensuing mushroom cloud. That would be really bad PR at the very least, and it would be a miracle if there wasn't any legal fallout as well.

So considering the worst case scenario...

...UNencrypted personal media collections are essentially just a nuisance, not an imminent legal disaster, in the grand scale of things. Everyone has files of "interesting" origin nowadays; it's the Internet. (A recent article on here noted how Spotify seeded their collection with media obtained from scene torrent releases.)

Plus, if your data is not encrypted, Amazon can deduplicate everything so much more easily as well - and considering that Amazon probably have a copy of near every possible permutation of data in existence (S3...), it's a whole lot easier to handle "I don't ever want this FLAC to go away" if you can use refcounting to do it. And no two encrypted files should ever match.

I realize I sound like a shill either/both for Amazon and/or the scary vulnerable kind of end-user transparency. I do feel weird recommending this. But I come from the standpoint of trying to figure out what's likeliest to actually work out in practice when using ACD. In the reddit example above, the majority of the data was not encrypted, and even though it was porn it went through fine.

That being said, I do have to admit I'm not quite ready to just go ahead and tell Amazon about the music or videos I've obtained, even though my collection is really tiny.