Earlier quoted context omitted.
That's why I suggested replacing at most 2 disks at the same time. But you could just one extra year and replace all of them one by one. Or you can just use some dumb & cheap storage backend (in the cloud) as an extra backup layer, which you can easily replace at any moment if costs go wild or it goes bankrupt, without having to change the user experience.
Right. It's possible to stagger your replacements so as to avoid bad batches, or even to buy from different vendors for additional diversity (although for SSDs you have much more divergent performance characteristics), but when you're talking about rotating disks one at a time that's a lot of non-negligible overhead. Depending on how much data you have to archive and frequency of access, it may very well be worth the…
And yes, my wife regularly looks at photos from 3,4,5 years ago, or older.