If you want to take the concept seriously, I recommend you see about finding old encyclopedias and old books predicting the future. Look at what they believed was "inevitable", look at how badly those predictions turned out. This will hopefully counteract the tendency the imagine the future by simply doing a first order extrapolation of present trends (Hi Michaelos).
This is, of course, assuming the goal is actually to make predictions that will at least resemble the future.
Speculation is important for forecasting; it's also fun. Speculation is usually conveyed in two forms: in the form of an argument, or encapsulated in fiction; each has their advantages, but both tend to be time-consuming. Presenting speculation in the form of an argument involves researching relevant background and formulating logical arguments. Presenting speculation in the form of fiction requires world-building and storytelling skills, but it can quickly give the reader an impression of the "big picture" implications of the speculation; this can be more effective at establishing the "emotional plausibility" of the speculation.
I suggest a storytelling medium which can combine attributes of both arguments and fiction, but requires less work than either. That is the "wikipedia article from the future." Fiction written by inexperienced sci-fi writers tends to generate into a speculative encyclopedia anyways--why not just admit that you want to write an encyclopedia in the first place? Post your "Wikipedia articles from the future" below.