I totally want the gene to control metallic objects :-) But I agree with you, at some point you will have to ask what species is this? Are you human or something else? I expect CRISPR to show up in athletes first, high risk/high gain and difficult to claim cheating.
From the RadioLab podcast linked above (excellent, btw), far more frightening in the long run: introduce genetic changes to the reproductive cells.
... which then automatically become part of any offspring.
... which are then automatically inherited by any subsequent generations.
And, new species.