Cool article, but the Cre/Loxp system will (most likely) never be used in a clinical setting for humans, at least not in the United States or anywhere with a decent regulatory body. Perhaps the biggest reason is that extra, non-native, sequences of DNA are being inserted into the genome (loxp sites). Even after removal with Cre, there is a "scar" that leaves behind one loxp site in the genome, which is considered a no-no.

As for wild-type CRISPR/Cas9 for the clinical setting, I think it inherently is dangerous to use because it can have a lot of unintended, off-target effects. My opinion is that the current state of CRISPR/Cas9 is good for quickly and cost-effectively investigating genetic modifications, but a more specific version or a new method of gene editing that is more specific would need to be used for high success rates, and low safety concerns, in a clinical setting.