Just because he hasn't personally done much in the way of personal experimentation doesn't mean he's not riding on a large volume of experimental evidence. Just using RDA values and all known micronutrients (not that his history has exactly been stellar in actually doing so) should get him almost all the way to where he wants his product to be.
(I'm really dubious of the carbohydrate he uses, though.)
And provided people are willing to eat a meal or two outside the system, their cravings should guide them to whatever nutrients it is they're lacking in.
So... I'm not sure I approve of the level of enthusiasm for the project that exists. But by the same token, I don't think the extreme pessimism is warranted, either.
The concept is good, but the methodology could have been significantly better. It has lots of potential, and the real danger is limited to those that will be consuming ONLY Soylent for extended periods. Using it to replace a meal or two a day, and having a complete meal every day, shouldn't be dangerous (I think).
What confuses me about the negativity is, what's so bad about the current situation? The earliest of adopters will serve as a giant trial, and if there are problems they'll come up there.
Also: people who intend to switch to JUST soylent should ...
Rob Rhinehart's food replacement Soylent now has a crowdfunding campaign.
If you're interested in one or more of these benefits, send in some money! There is also a new blog post.