There's a lot of nasty things that FinCEN potentially could do, but until they actually try it, there's not much basis to sue them.
I certainly didn't suggest suing them. Nobody I can think of would have standing to do it, since they haven't done anything and do not appear to be about to do anything. I was just pointing out they're the 800 pound gorilla in the room. May be calmly eating bananas at the moment, but you always worry maybe he'll decide to eat you instead. So maybe you don't set up a lemonade stand 20 feet from him.