actually there are dozens of ADHD type stimulants with meaningfully distinct properties that have prescribed (or studded) in humans. Far from having picked the low hanging fruit, the FDA just... stopped picking. For example, before Ketamine was approved, the last time the FDA approved an antidepressant with a new mechanism of action, was over 50 years ago. 

most of the limits we place on ourselves are self-imposed. Wimsey is the breaking of those bonds 

as I understand it, the AI capabilities necessary for Intelligence amplification via BCI already exist, and we simply need to show/encourage people how to start using it 

If a person were to provide a state-of-the-art model with a month's worth of their data typically collected by our eyes and ears and the ability to interject in real time in conversations via earbuds or speaker. 

Such an intervention wouldn't be the superhuman "team of geniuses in your datacenter" but it would be more helpful than even some of the best personal assistant's (and 100x less expensive). Especially when you consider adding new data inputs and outputs. Like biometrics EEG readings, TFUS (werable  non-invasive brain reading and brain stimulation), smart home devices and music generation.