Should posting articles based on obvious edits of existing articles (including notes indicating such) be encouraged, or discouraged? As an example, I had written up a rewrite of the Same-sex marriage in the United States article as 'Polymarriage in the United States', moved all dates forward 50 years, changed some of the case names... and then I realized I couldn't really tell if it was what snarles had in mind, or if he wanted more originality.
II think that should be OK - if you clearly indicate thus. And link the original.
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.