Last semester, in Advanced Poetry Writing, my professor Michael S. Harper spoke several times that the use of written or typewritten letters (as in, epistles) are dying out. And for him, this change is tragic. Authors' letters have been collected and printed in books for thousands of years. (For example, I believe the letters of famous Roman orator Cicero were collected and published soon after his death.) This long-standing tradition has a number of reasons. Firstly, good writers usually write well, even when writing casually; thus, the letters of writers, and especially those of poets, often have significant aesthetic or stylistic merit. Secondly, authors often write about their most important ideas and beliefs more casually in letters than in their formal publications, potentially giving readers a better understanding of their thoughts. Finally, authors reveal things about their personal lives through their letters that are often obscured, masked, or simply not discussed in other writings, and for those who consider these authors important, their personal lives are usually interesting as well.
So, why are written letters, so to speak, dying out? Technological advances, namely the computer and the internet, make hand-written or typewritten letters in a certain sense unpractical. Email is the basic communication tool of choice for much of modern business, not to mention academia. Email has a few significant differences from normal mail. Firstly, people are almost always less formal in an email than in a written letter. Traditional greetings and headings, for one, are not as widely recognized or thought appropriate in emails. Many emails do not even have greetings or signatures within the body of the text. Secondly, emails are naturally less malleable than a letter written by hand or by typewriter. You can't just throw a doodle into the corner of an email, and most emails don't even give you the opportunity to work with margins as a word processor program would. Finally, and most importantly, emails leave no papertrail. As most people do not print out their emails, and as many email services have automatic deletion of emails after a certain point, emails usually disappear after a time. Forgot any differences in the quality of the letters; there often won't even be letters for the collecting!
But here's where I think it starts to get interesting: while letters (and its byproduct, emails) will perhaps not be as prominent, other technological changes lead to opportunities that people hundreds of years ago probably couldn't even dream about. With a computer, huge amounts of information can be kept within an extremely small physical space. Consequently, I foresee the possibility that a famous person's personal computer space could easily become in the future open to the public, or at least to scholars.
Here's a really bad hypothetical which will give you an idea of what I'm implying: imagine famous poet Ezra Pound lived (technologically) during the 21st century instead the 20th. After he dies, DVD-Rs are produced and sold that contain all the writings typed on his computer. So, you can find 7 drafts of his "Sestina: Alteforte," random thoughts collected about what he wanted The Cantos to be, a bunch of really bad poems he would have deleted had he known it would seen by another human being, etc. You get his Mussolini desktop wallpaper complete with "DOWN WITH USURY" written on the bottom.
...I hope these examples are getting across the possibilities here. Given that people's personal journals have regularly been published in the past, I wouldn't be shocked if famous people's personal computer's data were made easily available past the time of their death, if there was anything interesting there to begin with. The truth is: since technologically it would be easy to do, it seems altogether possible.
I'm not going to argue how good or bad I find this possibility to be, at least in this post, but merely to suggest that it is possible.