Since the law specifically exempts the practitioner from any civil liability that could result from 'good faith' reporting, some may just go hog wild and error on the side of 'caution' more often than not.
I strongly suspect that this will quickly lead to a evaluative protocol.
MH practitioners in most jurisdictions already have a "must divulge" obligation in issues of perceived or expressed threat to others, as well as child welfare issues. Indeed, I believe that in virtually every jurisdiction in the United States, MH practitioners face criminal penalties for failure to report suspected child abuse or neglect.
The fact that they are required to make these reports however does not result in an automatic finding against the client, rather it results in an investigation of the claim by the State agency charged with that duty.
One of my responsibilities at one point during my career was teaching Mandated Reporting Policy to multi-jurisdictional law enforcement officers, medical and MH professionals, educators, etc. A common concern voiced was: "what if I come into contact with a child that I THINK is abused, but I'm not sure? I don't want to be responsible for having someone's child taken away mistakenly".
I used to explain to them that if they call in a report, it DOES NOT automatically result in any action other than an investigation of their concern... which, if they are truly concerned, is legitimate. Ultimately, it is the responsibility of the investigators to determine whether or not there is a substantial risk or an overt crime has occurred, and there must be a formal adversarial process if any action (criminal or civil) is taken.
My own concern is not so much the reporting protocols. The validity of any report can be investigated, contested, etc. Despite the fact that a mandated reporter might not face liability, if a professional repeatedly calls in bogus reports to law enforcement, or any other agency for that matter, bet on it that they will quickly be getting an earful (by telephone if they are lucky) one way or the other from highly PO'd and extremely busy investigators and their admin... been there, done that.
My concern is more that the State requires a FOID in the first place. I think that is the area that requires the most attention.