There are specific social networks around certain themes, but they might be one-sided and historical networks tend to focus too much on politics, religions and other conflictual questions or views, and not on history itself. A combination of several cultural themes might allow a broader spectrum of discussions, as history is often linked with geography and arts, cultures, nature, biodiversity, ecology and climatic conditions. Science is dealing increasingly with interdisciplinary programmes and projects, as all the different disciplines are more or less depending on each other.
It would be also useful to allow the sharing of classic (and modern) literature, poetry, music and good (clean) humour.
I agree with you that personal and private life, with selfies, dating, relationships, etc., should normally be limited to family, closest friends, school, work and specific interest groups on a small level (if needed by PM or in a separate, closed group) and not be disclosed to the greater public - for their own sake.