I think this in a very interesting theory, but I'm unsure of it's credibility. I think a lot of this is dependent on the individual, not the type/fixation of the individual. Certain trends may be found in certain types, I think that is very much a possibility, but ultimately the activity of certain neurotransmitters occuring in the brain will depend on the individual. A One won't necessarily have medium seratonin activity, low norepinephrine activity and medium dopamine - nor should it be assumed that s/he does.
This reminds me of how psychiatry is a field that is often put into question - there is no definitive test which determines if a person has a mental illness or not. Any 'definitive' decisions and diagnoses which are made are deduced from observation of the patient's behaviour, but no scientific tests which determine it from brain chemistry or whatnot. This means that determining whether or not this theory is correct is not going to be easy, hence why they haven't done so yet.
Also, I have difficulty believing that Instinctual Variant is the result of environmental factors, instead of just being inherent, especially considering how they've claimed that the Variant is the result of specific circumstances i.e. Sexual Variant people being the product of homes with a 'primary care-giver'. Don't know about that. Still, this is just an assumption I would make from my own experience, further observation and analysis may yield different findings.
We'll see.