Did GWAS collect data on subjective wellbeing? I have seen that they have some data on severe mental disorders, but that's not the same thing. I have wondered before about trying to collect a genomic database along with self-reported mood data, I think that would be massively useful, if it's been done I haven't seen it.

Yes, I saw that case. It seems that they were using an extremely high viral dosage. In my understanding one of the reasons AAV is typically used is the low immunogenicity at normal dosages and overall good safety profile. Obviously no pioneering method is without risk.

Whether mood disorders qualify under your criteria is debatable - certainly for a large proportion of people no currently available treatment is effective. Fatality rates may be relatively low, but I suspect a fairly large cohort of people living with mood disorders would rather tolerate some risk than live out the rest of their lives with no hope of treatment.

Definitely there's no single gene that controls mood, I think it's agreed that it's a combination of many factors, genetic and otherwise. But, strong correlations do exist between some alleles and subjective wellbeing. 5-HTT and FAAH are two genes with such alleles, off the top of my head.