Since the current debate is essentially pastoral, I doubt the question of papal infallibility is relevant. What is being attempted is a practical way to get around or ignore Church teaching on the Eucharist, rather than a redefining of that teaching.
Francis may well give the Germans the green light but he can't do it infallibly.
He seems to be slyly implying otherwise, and many poorly catechized Catholics will be duped by his sophistry.