NYTimes magazine has an article on gene drives, discussing the positives and negatives. Lots of concerns about negatives, particularly outside the scientific community.
In reading it I wondered: if I understand correctly, the gene drive consists of a genetic package which says: "if you find gene A, replace it with gene B and Crispr package X." So a gene drive spreads a gene throughout the population while also spreading the Crispr package needed to replace A by B.
So what did I wonder? Whether a gene drive isn't reversible, just do: "if you find gene B, replace it with gene A and Crispr package X"
Of course, it turns out any layman speculation I might have is out-of-date, witness this 2015 piece.