The technique sounds promising, since it avoids the typical problem of gene therapy, which is how to get CRISPR past the immune system into every cell in the body. With this technique you can do the CRISPR procedure in vitro.
A big downside to this treatment is that as far as I know this kind of chemo can make male patients infertile.
1) Extract bone marrow from patient
2) Use CRISPR to fix broken gene in the extracted bone marrow
3) Use chemo to destroy old bone marrow in patient
4) Transplant fixed bone marrow from step 2 back into the patient