It is not magesterial. It is simply an exhortation, which is merely the opinion of the Pope which is not news to most and is not binding.  The problem is that many do not know the difference and think Francis can change Doctrine: he cannot.  In order to prevent confusion on the indissolubly of marriage, the Cardinals are seeking clarification, as well they should.  Simply reading the responses on this cite, one can see the damage such ambiguity can cause.  Perhaps the Pope is not answering because he painted himself into a corner: he knows he can't change Doctrine and he can't defend chapter 8 of AL without either stepping over that line or having to retract his statements.  That's a fine pickle he got himself into.