AL, Footnote 301: "Hence it is can no longer simply be said that all those in any irregular situation are living in a state of mortal sin and are deprived of sanctifying grace."
It seems to me that Muller and AL (i.e. Francis) are arguing two different issues. Muller is saying that those living in "sinful situations" are not living in a state of grace and cannot receive Communion. I think Francis would happily assent to this statement because he's kicked the can further down the road.
Francis is saying in AL footnote 351 that what actually constitutes a "sinful situation" is no longer clear.
IOW, Muller is arguing theology and doctrine and Francis is arguing pastoral practicalities. Muller is saying that those living in mortal sin cannot receive Communion. Francis is saying..."Yeah we know. We haven't changed that doctrine as we keep telling you. We're just not sure who's actually living in mortal sin."
Muller is fanning the air here. In order attack this issue properly, he needs to 1) mention AL by name and it's problematic parts and 2) make clear that this exhortation cannot be used in the way both Schonborn and Francis said it could be used.
Pope Francis: I can say yes, period*. But it would be an answer that is too small. I recommend that you read the presentation of Cardinal Schonborn, who is a great theologian. He was the secretary for the Congregation of the Doctrine of the Faith, and he knows the doctrine of the faith well. In that presentation, your question will find an answer.
(Full Text of Pope Francis' in-flight interview from Lesbos to Rome, Catholic News Agency, April 16, 2016)
*The correct translation here is the word period. The translation from Catholic News Agency says many, but this is clearly a mistranslation of the Italian word punto, which Francis used.
As for Schonborn's presentation that Bergoglio recommends, the following excerpt which proves they are advocating a "de facto' ANYTHING GOES:
Schonborns Presentation of Amoris Laetitia
" In the sense of this via caritatis (AL 306), the Pope affirms, in a humble and simple manner, in a note (351) that the help of the sacraments may also be given in certain cases. But for this purpose he does not offer us case studies or recipes, but instead simply reminds us of two of his famous phrases: I want to remind priests that the confessional should not be a torture chamber but rather an encounter with the Lords mercy (EG 44), and the Eucharist is not a prize for the perfect but a powerful medicine and nourishment for the weak (EG 47)."
"Is it an excessive challenge for pastors, for spiritual guides and for communities if the discernment of situations is not regulated more precisely? Pope Francis acknowledges this concern: I understand those who prefer a more rigorous pastoral care which leaves no room for confusion (AL 308). However, he challenges this, remarking that We put so many conditions on mercy that we empty it of its concrete meaning and real significance. That is the worst way of watering down the Gospel (AL 311)."