Hoping this question pertains to historiography and so ignores the 20 year rule.
A lot of history is pulled from people who lived the events and their diaries or letters. How important will stuff like this be for future historians? Will e-mails from average, every day citizens be that important? Or diaries or text messages, etc? Or are we so well-documented at large that these smaller primary samples will not be so important?
Newspapers, books, articles, interviews the usual fare to cull through for primary resources is still mainly in the hands of the elite. Letters, diaries, and their modern associates (emails, texts, blog posts) pertain to the every day person. It also frames the narrative of the history differently. I believe that sources from the every day individual will continue to be important for future historians, especially those who would want to discuss/analyze societal trends and views.
The over abundance of sources will be a problem, since future historians will have way more material to sort through. You already see that in play now with most modern historians, especially those who work with 19th/20th century history.