For people of my generation, a great deal of history was seen on regular low-resolution TV. But a lot of it, up to the 70s or so (and often after) was shot on film, at higher resolution. Older generations saw some of this (once or twice) in newsreels at the movies.
So as HD sets become common, it would be great to see this old film footage of events like the wars, the Olympics, famous speeches, the moon landing and other space program material in high definition. I saw a DVD of the 1936 Olympics on a good screen and even that was surprising.
Some of this is already happening. HDNet is digitizing old sitcoms like Hogan’s Heroes, which was shot on film. Fun, but I think the life-changing events we’ve never truly seen (or rarely seen) at full resolution would be more important, and would also leave a legacy for education. And yes, that even includes that bad news, like the Challenger and the WTC.
Update: Discovery channel has an upcoming series of NASA footage coming up in HD. Now if only I could get discovery channel HD in a way that I can record without buying their proprietary box.