This is a one-off sentence, possibly far out of context, in a documentary that hasn't aired yet. This is not a formal teaching changing any current practice or doctrine of the Church. For better or worse, I think a lot of you are over-hyping this. I say this as somebody who would generally be in favor of civil unions as a "solution" for the Church in this matter.
I was going to write up a big effortpost to discuss what official church teachings are, what possible ways this can be reconciled with it as a prudential judgment (even if very tenuous and seemingly ill-advised), in what circumstances popes can be wrong about stuff, what Pope Francis's possible aims are, etc etc.
Then it was presented to me that "civil unions" is a questionable translation of what he said in Spanish.* And secondly, the sentences in that documentary the Pope is shown saying are spliced together from multiple interviews and weren't actually said in the sequence in which they were presented. If this is in fact fake news, it seems astonishing that it would get this far by simply being taken out of context and mistranslated, but the more digging I do, it really seems to be spliced at least.
*I've heard other sources saying that "civil unions" is a valid interpretation of "convivencia civil" but it seems to be somewhat ambiguous. A simple google search seems to take it to be "civil coexistence" in every context I can find. Unfortunately, nobody seems to have found the context from the second interview from which that sentence was plucked, as it is not from the same interview as the rest of the statement that is being quoted (that should raise some questions at the very least). Perhaps some of the Spanish speakers here could shed some light on whether "convivencia civil" strictly refers to civil unions or if it can have some broader meaning?
I would also like to know the difference between "civil union" and "civil coexistence" in Argentine law, assuming the latter even exists. Is there effectively any non-semantic difference between the two, much less compared to that between "civil unions" and "marriage", both of which are essentially the government acknowledging and protecting unions between individuals under the law, which exactly is what Pope Francis is being reported to have endorsed?
And this would still run contrary to the Vatican’s 2003 Congregation for the Doctrine of the Faith, which directly states that homosexual unions cannot be legally recognized. I don't know if the Pope has unilateral authority to change that doctrine (although it was written at the direction of JPII), but even still, the Pope taking an alternative perspective to church teaching certainly casts ambiguity as to the Church's real stance.