> I mean, really, is there any possible reality that involves the NSA/GCHQ deleting the mountains of data they have surreptitiously recorded?

They will: it costs a lot of money to keep data alive.

And it is a shame, NSA data for research purpose should be put under the UNO protection: - it holds lower bits of informations interlaced with the "big data" like how flu is propagating; - we could analyse causality chains and propagation of ideas (the impact of culture); - we could see corruptions effects, measure it and decide if it worths the price; - we can record the variation and evolution of natural langage/style;

These data are a treasure, the should be opened after X years, but for economic reason, they will be deleted.