I believe that over time doctors will cease with the labels such as "inattentive ADHD", and merely treat debilitating inattentiveness based on the individual. The fact that ADHD can be hyperactive or inattentive, has always seemed bizarre to me. One person can't sit still, but my problem is I can sit still to a fault. But we have the same underlying disorder that's treated with the same medications.
The number of types of clinical depression, for example, is absurd. It's not merely depression, it's bipolar disorder. It's not merely bipolar disorder, it's bipolar disorder type II. Seriously? Decades from now we're going to regard this approach as highly primitive and bordering on pseudo-scientific.
Because every brain is different, trying to strictly classify these disorders would force people outside of a category, but the other side of that is that we have schizophrenia which seems incredibly broad "junk-drawer" sort of classification, to the point where it's easy to imagine someone who is highly eccentric being misdiagnosed.
I have no credentials obviously so this is all baseless conjecture.