I'm a little confused about this part. Does the Online Safety Act create personal liabilities for site operators (EDIT: to clarify: would a corporation not be sufficient protection)? Or are they referring to harassment they'd receive from disgruntled users?
Also, this is the first I've heard of Microcosm. It looks like some nice forum software and one I maybe would've considered for future projects. Shame to see it go.
This seems very plausible to me, given what they and other moderators have said about the lengths some people will go to online when they feel antagonised.
In the same way that you could be sued for anything, I'm sure you could also be dragged to court for things like that under this law... And probably under existing laws, too.
That doesn't mean you'll lose, though. It just means you're out some time and money and stress.