Yes, I was also thinking about perkeep and giving it a spin. I was considering a RAID 1 array for redundancy.
Another thing I was considering was M-Disk[1], that can, supposedly, hold information for 1000 years. But I wonder what other people's experience with it is.
Alternatively, I understand normal Blu-Ray disks should be able to have data retention of about 40 years, and that sounds decent to me.
I was looking into Amazon glacier and/or google cold line, and the prices seem decent, but I do not like the fact that you have to pay monthly, even if a small sum, it's just one more thing to concern yourself with. I would like to prepay and know my stuff is up there for a couple of years.
Normal Dropbox/Google drive stuff is too expensive to store big amounts of data, so not worth it. Plus, you have a copy of it locally also, (at least in normal use cases)
Thinking about it, I think this would be a great idea for a startup. Cheap data storage for long term storage, with competitive prices, the ability to per-pay, user-side encryption and a simple UI that grandma can use to drop photos. It should be able to guarantee that the information you desire to will outlive you.
[1] https://en.wikipedia.org/wiki/M-DISC