It's not easy to attract an effective class-action lawsuit unless there's a lot of money in it for the law firm itself. Think of all the truly nasty chemicals which go into electronics and biotech effluent. They have their own big legal departments.
I think the ingredient was already banned in the EU. That would trigger suspicion on this side of the pond too. A mere case of individual sickness could easily be attributed to sensitization or careless handling - which would potentially apply to every kind of color development! Lots of people have developed hyper-sensitivity to RA4 chem, for example, or Ciba bleach.... not to mention metol, which can be thought of as powdered poison oak in a jar once one gets sensitized.
But I was walking around a local lake a couple days ago and encountered a big rental herd of goats behind a portable electric fence, chomping down poison oak leaves as if it were butter lettuce salad, and even eating thorny wild blackberry vines. Maybe those goats should be hired for photo lab work as well.