Thinking out loud, I think the reason those salons became famous is because the participants published, and their publications got a lot of attention. An example that springs to my mind is the Vienna Circle. But maybe a better example is Madame Geoffrin’s salon which hosted French nobles and Enlightenment thinkers. In that case too the attendees either published, or were powerful figures in society.

The format is a smallish group of people discussing ideas, probably with some connecting theme. It seems like historically those themes were broad, like “philosophy”, with a focus on debate. If some of the people involved turn out to be important to society you’ve got yourself a historically-significant organization. If not then hopefully everyone had a good time.

What are historical salons?

You mean like the collections of artists/authors?

historical salons

Historical Slaloms? Historical Saloons? Historical Salamanders?