The CWAL Rubber Room
"I tied you up while you were talking."
Disclaimer: This is all from memory, five years out of date, and from an undergrad course. So if Snapper or Friendly show up and contradict me, listen to them.
So even before CRISPR/Cas9 became the hip new thing, it was possible to do gene edits in a living cell. They were just... kinda error prone. But whatever, CRISPR makes that step more reliable and it's great but not the only thing you need to be doing.
So to make gene editing useful you've gotta get the edited copy into a large enough proportion of the cell population that's important for whatever you're trying to do. I don't really know how well anyone's done at mass gene editing in-vivo but that's probably pretty early stages (I think techniques in this neighbourhood are being attempted for cancer treatment right now, which would be an early phase in development because you don't care so much how much damage you do to the cancer cells in the process). So if you wanted to gene-edit, say, your muscles, you're waiting on that and it's probably gonna be a while.
What they have done successfully in animal models is gene-editing therapy for diseases that occur in tissue that regenerates. The example we looked at was curing sickle cell disease in a mouse. In that case, you don't need to reprogram all the bone marrow cells (which are what generates red blood cells which express the disease), you just need a bit of fixed bone marrow stem cells then you can nuke what's there and replace it (like a bone marrow transplant, but with a self-donor so there's no worry of rejection).
For this, you need to take a cell from the adult mouse, reprogram it into a stem cell (what's called an Induced Pluripotent Stem Cell, or IPS cell), alter its sickle-cell globin gene into its normal form (a single DNA base pair change), then induce it to turn into a bone marrow stem cell, then you can implant it and it grows into bone marrow that produces correct red blood cells.
The problem is that first step of making the IPS cell, which involves throwing a bunch of chemical triggers (actually I think it's only four of them, I don't remember what they are) at the cell that are important signalling molecules in developmental processes. And since we don't fully understand how or why this works, the resulting cell (and its progeny) can very likely end up in an "unstable" state (for lack of a better term coming to mind). And when developmental pathways are disturbed, cancer is the common result.
So essentially, we can cure sickle-cell anemia in exchange for probably giving the patient blood cancer and that was (afaik) the rough state-of-the-art five years ago. Extrapolate from there how likely you estimate it is that you'll be doing anything useful or cool in the near future.