I think, Peter, that decent priests hearing of in a crime in confession, will do what they do now - do their best to persuade the penitent that the information must be revealed to government authorities, but respect the penitent's wishes in the end.
In most cases, the outcome would be the same, with or without the law - but if push comes to shove, priests will honor the seal of confession.

Jack, I appreciate your insights. As some of you may know, I worked as a U.S. government investigator for 25 years, doing background investigations on applicants for government security clearances. If we came across information that the applicant had received counseling or psychiatric treatment, we had to interview the counselor and obtain treatment records. We had to first obtain a release form signed by the applicant, but most applicants signed the form without hesistation because they wanted the job they were being investigated for.

But personally, I felt this was an undue violation of the sacredness of the counselor-client relationship. I hated this task but I did was I was supposed to do, although I tried do do it with as much respect for the applicant's privacy as I could muster.

-Joe-