The main ingredients in Soylent (which contribute to the macros) are the fats (canola and algal oil), the protein (rice protein), maltodextrin (from corn starch), and oat flour.
Oat flour is just ground oats, and will be high in purines, just like oats. If you suffer from gout and are sensitive to purines, it's definitely a concern - a major ingredient known to be high in purines in a food product you eat all day is a recipe for trouble.
rice / rice protein - low in purines
maltodextrin / starch / corn - low in purines
canola oil - seems low in purines, but I'm not happy with my sources
algal oil - I really don't know, and I'm not easily finding the answer from reputable sources.
Anybody find a hit on algal oil, one way or the other? Refined fish oil is low in purines, even though fish flesh is high in purines, but I'm not clear on algal-sourced oil.
For conditions like gout, I think the reason it seems very variable is because as individuals, we're very bad at taking everything into account. One person says sardines are killer, another says they're not bothered... but maybe the person that's not bothered only has a little bit with some cracker, while the person who has problems with sardines likes to eat a whole tin of them while chatting with friends over a couple of beers... but that's a lot more sardines, and the beer is a problem, too!
The other thing to remember is that most foods contain purines. It's just a question of the level in each. It's generally a mistake to focus just on one thing you ate if you have an attack - everything you ate was contributing to the overall load. Gout isn't a response to a particular food, it's a response to the overall purine level (and to the other things that contribute to uric acid, like fructose.) If someone eats a lot of moderate-purine foods and tops it off with some liver pate, maybe they have a problem. But if someone else eats a lot of low-purine foods and tops off with the same liver pate, maybe they're OK.