Ah, the arrogance of youth. Of course the NSA doesn't anticipate storing a yottabyte now. But facilities of this size are intended to have an operational lifespan measures in decades. In the ~30 years since I got my first computer my available local storage has grown from kilobytes to terabytes. I sometimes work on petabyte-scale projects now and I can conceive of exabyte applications easily (google is rumored to be in that league already). I feel pretty confident that $250 will buy you a petabyte of storage for your desk by 2025.
So having seen a billionfold increase in what I can affordably hang off my personal computer, I'm not willing to rule out another one over the same timeframe.
YEARS ago, the electronics company "Phillips" who invented the CD made a prototype of a new format that used "wave division multiplexing".
In short a full-spectrum laser (not red or blue or green) with 16.8 million colours was used, that could read data from a disc, using multi layers read via every "colour".
So in essence it would turn a 9GB disc into a 9 x 16.8 million GB disc.
Or 15200000 GB disc.
The Technology was shown working to trade insiders (myself being one of them) and then....
It just disappeared, never to be heard of again..
Some colleagues speculated that Government or Military wanted the tech and approached Phillips.
So having seen a billionfold increase in what I can affordably hang off my personal computer, I'm not willing to rule out another one over the same timeframe.