A very interesting and comprehensive post. I really like the concept of molecular memory. Biology has used this kind of memory since it started. The classical examples would be retinal in our eyes. The light changes the bonds from 11-cis retinal to all trans retinal. Though is temporary. But other examples include phosphorylation of proteins and methylation of genes. The methylation and demethylation of genes is form of a genetic memory (epigenetics) which switches the genes on and off or may even act as subtle regulator of gene expression. I think biomemtics can also serve a way to make molecular memories. This got me thinking of very old article on using bacterial rhodopsin for making electronic or photonic devices, and even holographic memory chips. See this for example. Anyhow, really liked this post. Hope to see this field develop well in near future.