One of the most important things is the form of Vitamins, I don’t see anybody paying attention to this, not even Rob.
For example you can read here, why is important to take the right form of a vitamin, not all the forms are equally good and some of them can be even harmful.
Common Synthetic Vitamins to Avoid and Other Toxic Ingredients to Avoid In Supplements
Some of the multivitamins that people is using for soylent contain vitamins mention above.
Synthetic vs Natural vitamins
Also it wouldn’t be a bad idea to think about to exceed a little (200%) the recomended ammounts for water soluble vitamins
I really think that @rob or somebody from his team should research a little bit more about this and come out with the best forms and combination (some forms can reduce the assimilation of others) of vitamins for Soylent. Now they have been funded they could hire a chemist or a nutritionist to do this.