Right, as long as you store it in a format that you choose for compatibility then text will be fine on that front. Even if you don't have a proper ODF reader it's still a zip archive with text files inside. And UTF-8 is easy to decode.

The problem as I see it is defending from two possible problems at the same time: having the media fail, and being hacked. Some kind of internet-based storage is great for the former, lousy for the latter. But with a bit of effort you can combine online distributed storage with a closet or two full of hard drives and tapes.