That would be a fucking travesty if the US government did that (and I think the forum is hosted in the US, so they'd be the ones shutting it down), and I wouldn't put it past them to at least make threats to do so if all mentions of mixers weren't scrubbed per their request.  They're being bullies with regard to crypto in general and mixers in particular lately, and to your point it is quite disheartening to see a change like this being made that strays so far from the spirit of what bitcoin stands for....but try to fight the government, and you're basically guaranteed to go bankrupt or lose anyway.

On the other hand, at least we've got some decision being made instead of a bunch of wild speculation and fear about what might happen with mixers and our beloved forum.