It just seems like it would be a really cool thing to have gills and be able to populate the oceans in the same way we populate the land. We could have houses and shops and vehicles, andgo on walks/swims and just kind of live underwater.
Start a whole new second species of human here on earth maybe, Who knows?
Yes, but being able to change genetic code does not mean being able to design entire organs and pop 'em in there during fetal development. That would be very challenging.
Gene editing has the most positive potential when it comes to things like curing/eradicating genetic diseases, doing microbiological research, or engineering metabolic products in microorgsnisms.
probably yes, if we accept the mountains of dead human babies the research would inevitably produce.
Pretty sure you can already get those you just need to have sex with enough siblings and cousins
Yes, but not very good ones, probably. We're endotherms (hot blooded), and as a result we burn like 3 times as much oxygen as a similarly-sized shark. You'd need a lot of gills.
The rest of our body is also not very well suited to being underwater long-term. If you're adding gills you might as well change our silhouette, eyes, hair and skin as well, but you might not look very human afterwards. Maybe you could manage something merperson-ish, with an extra-flexible neck for looking towards where you swim and gills all along the tail? Sanitation would also be a bit of a nightmare, because if there's a sewage leak you get to breathe it.
The other option is just to get really good at diving conventionally, maybe enhance ourselves to make that easier, and build dry "indoor" spaces underwater. The technology to do it at a basic level isn't new, but there just hasn't been much interest in living that way yet.
Human embryos do have immature gills, but they are reused to create ears, jaw, tonsils, thymus, parathyroids and the large arteries in the neck and upper chest. We could add extra pairs and try to turn them into actual gills, although that would require removing the aortic arch and forcing all blood through the gills. Connecting them to the pulmonary system is not possible, as lungs and gills need different pressures (that's the whole reason we have two circuits). Maybe we could connect them in parallel to the aorta? That would only work as a backup, but with an adequate vasomotor system could do a nice job!
Its funny I did a paper on CRISPR in highschool and was very interested in the technology and one of the possible uses I mentioned was giving people gills to live underwater.