Experiments of this general sort have already been done. I haven't read deeply yet, but exploring the biblio it appears that the novelty here is that something that worked in animal models by a semi-well-understood mechanism was demonstrated to also work in humans via mere oral administration of an already FDA-approved substance.

Epigenetic treatments of adult rats promote recovery from visual acuity deficits induced by long-term monocular deprivation

We found that chronic intraperitoneal administration of valproic acid or sodium butyrate (two different histone deacetylases inhibitors) to long-term monocularly deprived adult rats coupled with reverse lid-suturing caused a complete recovery of visual acuity, tested electrophysiologically and behaviorally. Thus, manipulations of the epigenetic machinery can be used to promote functional recovery from early alterations of sensory input in the adult cortex.

I'd bet the learning effect is quite generic but I suspect that most of the things that would be really useful for humans would take some pedagogic intervention, and designing the post-administration training process is probably a non-trivial task. Something I'd bet would probably work is building up great smell/chemistry associations ("this smells like it has a ring with a sulfur in it") but even collecting a lot of different samples and their chemical structures for paired presentation would take a bunch of work.

I think the smell example sort of illustrates some of the other limits... Just as with Anki, a non-obvious hard part is simply figuring out what things are even worth the effort of tracking down, leaving aside whether they should be acquired, retained, and folded deep into one's neural circuitry.