What restraints do you envision the bishops can put on such individuals? What avenues do they have open to them? How would such "lunatic fringe" individuals respond to the imposition of these measures?
Chocks Away - face up to it. They did the most sensible and politically the most neutral thing. In answer to your original question, they didn't overstep the mark.
It would seem to me that in your eyes it is a case of damned if you do and damned if you don't. If they had kept their mouths shut and allowed Cóir et al to pretend to be their mouthpiece you would have believed them to be making a political statement. By explicitly distancing themselves from such organisations and stating categorically that they take no position on it and that it is a political matter for individual catholics to decide you accuse them of interfering.
I can only assume from all of that that your only preference in the matter is that they disappear altogether - hardly an unbiased position to start from in commenting on them.
Well said.