This question really irks me. To be honest, I have been irked by it since I was first asked to contribute a post, and I'm afraid I've annoyed Jamie by persistently asking her for a clearer formulation of the topic. But now that I've given it some thought, and eliminated other possible sources of irritation that I first needed to consider (eg., the syntax is confusing; the question is too broad; the question is really two different questions; I'm too busy for this; I'm too old for this, etc.), I think I may know the problem: the question is naive.
We do not build cohorts and communities, digital, scholarly or otherwise. Rather, they build us. They build the way we think—our sense-making strategies—and the way we formulate problems and questions, the way we go about seeking solutions, the way we do our work, the way we shape our pedagogy, the way we interact as colleagues and professionals. It's nice to think that our higher education industry, which has linked its fortunes to digital modes of content delivery and the management of learning outcomes, grants us agency in the building of cohort. But as I read the very smart posts that have been contributed by others to this topic, certain words tend to recur: chaotic, messy, unpredictable, complex, newness. In fact, it seems that we have yet to understand the ways that digitization may (or may not) enable us to build online cohorts and scholarly communities, and the reason may not be that we haven't talked about the problem enough in forums such as this one, or we haven't lived it long enough to feel confident in our abilities to grab the reigns of social media platforms and software designed to make us feel that we're driving the bus, making choices, and exercising autonomy in building our intellectual networks. Another possibility is that scholars and the communities that produce them are currently being remade by the economic stresses, technological solutions, and social stratification that are remaking the 21st century university and the academic administrative managerial class—the cultural laborers who will publish the great essays and books about digital cohort, and hand over all rights to digital libraries that will then sell our work back to the members of our cohort for a fee.
For literary scholars of my generation, the process of academic professionalization began in graduate school where we found one another as a result of chance, love, and politics. For the online students of today and of the future it will happen pretty much the same way, I bet. Very little, it seems to me, happens by design. And the design part is probably the least interesting of all for me. So maybe we should not ask ourselves how to build digital cohorts and academic communities. Maybe we should ask ourselves how best to intervene in the industrial processes that are slowly but surely rebuilding us.