My understanding is that Zimmerman thinks that good history makes a compelling argument about humans in time. It might be compelling in that it is a story told well, and, most importantly, it casts light upon bigger historical themes. There is a relationship between the specificity of the project and the generality of its historical context. For example, to describe the Wikipedia's coverage of 9/11 is just that: descriptive. But a historical argument should also say something more. (Otherwise, the description might only be of interest to the narrowest archivist.) What does the coverage of 9/11 tell us about the event, about new media, or even the development of the Wikipedia? The specific historical research and argument needs to relate to the general -- and often taken for granted -- themes: to augment, support, or counter. However, one must also guard against presentism, to draw connections between the past and present. This often will be compelling, and sometimes useful, but it can also turn into a fishing expedition in order to justify how the author feels about the present, instead of a deepening of our understanding of the past.
Later: In my own draft paper, I did not address the question of what is different about the Wikipedia vision, and that of, say, H. G. Wells.Or, what does HG Wells tells about the Wikipedia? What is new and novel with the Wiki, why did Wikis happen when they did? What are the new assumptions brought by use of the Wiki? None of the projects I looked at were used to describe the cultural space from which they came. It can be useful to pose this question to oneself: what does the Wikipedia tell a future historian about our present time?