Check out the Utah Data Center [1]. They are already creating storage on the order of exabytes in a single facility. As storage technology improves, we can expect to see that capacity grow rapidly. Assuming they retain the data, over time it would be declassified and made legally available. The big question is whether or not they retain it. At the minimum, I doubt they'd even consider deleting anything until current encryption is cracked to enable them to decrypt the bulk 'line tap' style collections.

[1] - https://en.wikipedia.org/wiki/Utah_Data_Center