CRISPR biologist here, albeit in far more interested in CRISPR as a microbial immune system, and the bulk of my work has been examining CRISPR-associated Rossma

CRISPR biologist here, albeit in far more interested in CRISPR as a microbial immune system, and the bulk of my work has been examining CRISPR-associated Rossman fold proteins, not Type 2/Cas9 that is used for genetic engineering. However, I still have a fairly large working knowledge of the field and I guess I could be considered something of a tangential expert, at least compared to journalists and lay people. In short, there are huge limitations. The first issue is how to edit people reliably. Cas9 simply isn't accurate nearly enough of the time. It's not a system that could be employed in a living human being without risking mistarget effects. How severe those would be is something that still isn't known, and would be difficult to model because where you miss would likely depend on the target gene. There's a few thought processes on how to do it more safely. One is to make the edits in lab, verify the changes, propagate them. This is by far the safest route, but leaves other issues. How do you propagate the changes? We don't know how to propagate the changes to an adult human whatsoever. Stem cells get floated but that's still an underexplored field so it's difficult to say what's going to happen, or if it's even possible. Regarding that to put in, that's the easy part. We've been designing sequences for artificial proteins for decades. Researchers at CalTech just published a paper last November where they designed a system of viral proteases (proteins that chop up other proteins) in such a way that they could perform logic circuits in a living cell, and do things like kill the cell if it developed cancer. The first things to come will be targeted drug delivery, biomarkers, and cancer prevention. However we are still a long way from propagating changes throughout an adult human, if it's even even possible with CRISPR.