You’re definitely right how this without proper regulation could get out of hand with unethical individuals trying to edit genes. I’d say from my non-geneticist perspective the line would be “would editing this gene improve the individual’s quality of life or improve their life expectancy”. Operationalizing"quality of life" is obviously crucial here and can’t be defined socially but medically such as “no debilitating pain”.

I do wonder how things like this will impact existing communities of individuals with disabilities. I’d expect it would probably increase discrimination as it will increase the perception of people with disabilities as being “curable” which isn’t always possible or even desirable.