Most, if not all of the nootropics out there are so-called "small molecule" drugs; their relatively simple molecular structure lends itself to easy synthesis (but wide-ranging, unpredictable effects within the human body).

Pharmaceuticals (and hopefully nootropics) in general are progressing toward more "large molecule" medicines (or "biologics" as this informative page on Bayer's site terms) that are much harder to design and manufacture, but have a more directed/precise effect within the human body.

All of the top "new" nootropics gwern listed (except phenylpiracetam) are peptides, which qualify as "large molecule"s. But, while we stumbled across many of those, in the future it should be feasible to design targeted peptides, taking into account the receptors we'd like to target, thus having fine-grained control over the effect of the drug.

The problem is that there are too many regulations and not nearly enough money in "nootropics" to attract the investment necessary develop a targeted nootropic peptide from the ground-up.