I agree. I would expect that in general the microbiome results are going to be pretty much on par with most of the population and generally not that interesting. However, two interesting questions can be tested on people who are getting a large portion of their diet from Soylent. The first is, does the Soylent user base have a different microbiome that the rest of the population. If not, then more positive news for Soylent. If so, then what is it that is causing it? Is it beneficial or detrimental? The second question is does the microbiome change when the calorie source is more homogeneous than the typical diet, and if so what do those changes mean.
I also agree that the field is too young to produce any interesting results. However, for the field to move forward the field will need data. The Soylent crowd is a great test bed to compare diet and microbiome effects. A few people, consuming most of their calories from Soylent, profiling their gut microbe every few months; that might be a nice little data set to start cracking into some of these questions.