What do you expect will happen? Do you think lots of people are going to get very sick by going on a Soylent-only diet immediately, not monitoring their health closely, and ending up with serious nutritional deficiencies? That's one of the more negative scenario, but I honestly don't know how likely that is. I think people are likely to do at least one of three things:
Then again, I may have too much confidence in people's common sense. Rob is definitely marketing it as a finished product and a miracle solution.
I think there will be a range of issues from a few diehards hitting serious issues to people just having low-grade issues which they don't notice because they won't be randomizing blocks, effects similar to the hedonic treadmill will make it hard to compare over time, they'll get initial benefits from the usual placebo/Hawthorne/overjustification effects, and subjective self-rating has many known loopholes where you can think you're getting better even as you're actually getting worse - but regardless of the exact distribution or what the worst-cases look like, we won't know for the reasons I list above.
Instead, we'll get another internet circle-jerk about how Soylent is awesome and the critics are wrong.
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.