As sad as it is, video is already a preferred and main content format for most people. It always was. The closer to reality, the more engaging [EDIT: and easier to digest] the content. We had some text renaissance due to technical limitations, but that's over already. Beginner programmers now routinely shun written content in favor of video - how contradictory is that? But that's how it is right now.
Writing as a mode of communication requires effort on both the creator and consumer sides. That effort has many positive side effects, which is why some people still favor it [EDIT: and will favor it for a long time in the future, until something genuinely better shows up]. The problem is that, no matter what, effort is still effort, and people generally don't like to exhaust themselves. Gyms would be chock-full, and we'd have no obesity problem if it weren't so.
Your "century from now" estimate is extremely optimistic, to the point of being completely divorced from reality. If I had to bet, I'd say we will lose most textual content from mainstream consumption in the next 5 to 10 years. My guess is that writing will become the equivalent of today's HTML and JavaScript: a source code to be interpreted by the machine to produce a visual representation that people will consume. It'll disappear into the background and will only be touched by professionals.