Take a look at Robins v. Pruneyard Shopping Center for an interesting case that set precedent in California. The CA courts have determined that certain areas of shopping malls are designed and used for public congregation – the modern equivalent of the town square – and should thus be treated as public for a for purposes of First Amendment analysis, which means that a much higher standard applies to speech restrictions in these areas.

This standard could be applied to privately-owned online "town squares" in future decisions.