They are not telling us what is going to be in the documentary. What they have told us is not very interesting.
What Comes Next Is the Future is a story about the internet, and how the shifting mobile landscape has drastically changed our industry. But it's also the story of how we've all changed as a culture and what we can look forward to in the future, as seen from the perspective those who've helped build and shape the web over the last 25 years.
What isn't interesting to you doesn't mean it's not interesting to someone else. Personally, I'd be deeply interested in seeing a video of those who founded http / site conventions talk about mobile platforms, cloud computing, and other ideas for the future!