I would disagree with you. I think that already exists.
In terms of the ability for the Attorney General to make a dangerous offender designation, that application comes from the Attorney General's office, but the decision is ultimately made by the judge. For a dangerous offender designation, the offender remains in custody indefinitely so long as that offender is deemed a threat. The long-term offender designation carries not an indeterminate length but it has a much greater custodial and punitive aspect to it.
So I wonder whether that doesn't already exist.