Generally speaking, I believe a man has the obligation to marry a woman if he gets her pregnant. I understand there are circumstances in which this would be inadvisable or even impossible, but for the pope to specifically request a couple with the arrangement in question in scandalous, because to many observers, it smacks of implicit approval of irregular situations that should, in fact, be strongly discouraged.
The way this is (predictably) being portrayed as a "taboo-challenging" ceremony is guaranteed to create the false impression among many observers that the Church's teachings are "evolving" in response to the on-going moral depredation of the surrounding culture.
True "mercy" requires that Francis and his handlers not shirk their responsibility to communicate Church teachings in full.
Your judgment reflects prejudice.