I know hunches don't count for anything on HN, and we still don't have enough information, and may never. But I think this is right, they're storing all major forms of communication. If so, it's incredibly dangerous.
I think it's absolutely thrilling. Just imagine, all it takes is one disgruntled, lucky cypherpunk to crack into the NSA content database and reveal its content to all.
Unencrypted emails, text messages, phone calls between you and your mum. Let's be honest, leaking that database is probably what it's going to take to see any kind of real attention/change on this issue.
EDIT: Possibly http://www.nytimes.com/2013/06/11/us/how-edward-j-snowden-or... "Mr. Snowden has now turned over archives of “thousands” of documents, according to Mr. Greenwald, and “dozens” are newsworthy."