Wow, this is a really cool question!
I think the biggest advances will come in the form of manipulating fatty acid composition of the cell membrane to enhance anabolism.
As far as nutrients and workout nutrition, this is a tough call... I remember too that I used to consume rice cakes PWO and thgouth I was badass (because Duchaine told me to do so). LOL
Now, I'm not sure we actually WANT to illicit a greater insulin spike than the one we already get, and I'm not sure that amino acids can be mode MORE anabolic.
Maybe something will sensitize our body to become more receptive to the amino acid-induced stimulation of protein synthesis.
There may also be better ways of replenishing glycogen, but this would mainly affect athletes in competition.