1. Soylent doesn't seem to be entirely based on fine chemicals. When you go through their ingredients list, "fish oil", "oat flour" and "rice protein" likely contain a lot of the "(nonessential) nutrients" you fear missing out on.

I still wouldn't want to be the guinea pig to exclusively live off of Soylent.

2+3. Having said that, there is plenty of research on "Total Parenteral Nutrition" and "Enteral Nutrition" for those that cannot consume regular foods for medical reasons. It isn't exactly a solved problem however, there are still issues.