Paragraph 2 seems to be the most problematic:

2. This Vatican Council declares that the human person has a right to religious freedom. This freedom means that all men are to be immune from coercion on the part of individuals or of social groups and of any human power, in such wise that no one is to be forced to act in a manner contrary to his own beliefs, whether privately or publicly, whether alone or in association with others, within due limits.

The council further declares that the right to religious freedom has its foundation in the very dignity of the human person as this dignity is known through the revealed word of God and by reason itself.(2) This right of the human person to religious freedom is to be recognized in the constitutional law whereby society is governed and thus it is to become a civil right.

It is in accordance with their dignity as persons-that is, beings endowed with reason and free will and therefore privileged to bear personal responsibility-that all men should be at once impelled by nature and also bound by a moral obligation to seek the truth, especially religious truth. They are also bound to adhere to the truth, once it is known, and to order their whole lives in accord with the demands of truth However, men cannot discharge these obligations in a manner in keeping with their own nature unless they enjoy immunity from external coercion as well as psychological freedom. Therefore the right to religious freedom has its foundation not in the subjective disposition of the person, but in his very nature. In consequence, the right to this immunity continues to exist even in those who do not live up to their obligation of seeking the truth and adhering to it and the exercise of this right is not to be impeded, provided that just public order be observed.

The above text would not, in my opinion, ever apply to Catholic monarchs, even if, by some miraculous outcome, a Catholic monarchy would come into existence at some point in the future.  Since a Catholic monarch would be consecrated by the Church (as occurred in the past), the monarch would not govern as some "human power," but by divine right.  Furthermore, a "just public order" in a Catholic monarchy would include the "salvation of souls" as being the highest "moral obligation," so a Catholic monarch could morally suppress anything (or anyone) that was endangering the eternal salvation of his Catholic subjects, hence, the "within due limits."

I messed-up the title on my OP -- I had meant to say "Thoughts on Dignitatis humanae."  (Oops.)