Sounds like they would need to know how to grow massive amounts of these cells in culture for this to be viable. As others have noted here, only about 20% of th

Sounds like they would need to know how to grow massive amounts of these cells in culture for this to be viable. As others have noted here, only about 20% of the cells get the desired fix and many cells die in the process of getting the fix. Cell culture of human and stem cells is non-trivial and rarely gets done on a large scale. Most of the time you have to grow cells in a petri-dish which in practice means you get very low cell density (number of cells per volume of space it takes to culture the cell i.e. the stacking of the petri dish, the 2D surface they occupy in that dish, how dense the cells like to get within that dish before dying etc.). Ideally you want to grow things to high density in a medium where the cells can out-compete all contaminants. One example is yeast fermentation, the yeast outcompetes everything. Another is e-coli in the lab, where the coli grows faster than most anything in the culture. All of these are liquid suspensions, not on dishes. In this case, we're talking about a blood disease, so you may be able to grow the cells in liquid culture. You also have easy access to a lot of them (blood is pretty easy to get, in contrast to say, brain). This is where CRISPR is most likely to show results in the clinic in the near future, but there are still lots of hurdles to overcome.