I recently learned about flaxseed oil [from the same plant as linseed oil (flax), but made by a different process], which apparently has a desirable fat profile, having at least a 4:1 ratio of omega-3 to omega-6 fatty acids . With one tablespoon (nearly 15 mL), you get approximately 8 g of omega-3 fatty acids . That appears to be more than what’s provided Soylent’s 1.0 formula via the canola oil and fish oil :
Soylent contains roughly 1g of each omega-3 fatty acid per day…
I assume by “each”, the macronutrient overview  means of omega-3, EPA, and DHA. Unlike fish oils, flaxseed oil does not contain raw EPA and DHA (the products of our bodies processing omega-3 fatty acids). According to the macronutrient overview  and Wikipedia  (I will neglect linking all the original sources), this processing happens inefficiently in the human body, at around 5%. I don’t have the expertise to say whether 8 g of short-chain omega-3 fatty acids + the time of typical bowel cycles (affecting intake) + the 5% conversion is acceptable for the amount of EPA and DHA humans need. (By the way, fish don’t actually make most of their own EPA and DHA: they get it from eating algae .)
I have not tried flaxseed oil myself (since I just learned about it), but cursory searching suggests it is not the most palatable of oils [Google, Bing, whatever search engine : “flaxseed oil taste”]. This issue is encountered when eating/drinking flaxseed straight. I would presume that eating/drinking a mixture of canola oil and fish oil is likewise unpalatable, but one is probably better tasting than the other. I would also presume that mixing 1 tablespoon of unpalatable oil with a day’s worth of Soylent would dilute it enough that it wouldn’t be noticeable. Can anyone with firsthand experience with flaxseed oil and/or an oil mixture like Soylent’s comment on this?
On Amazon, flaxseed oil  is about 2 times more expensive than canola oil . I assume this relationship holds with wholesale suppliers, but I don’t have access to such information. I couldn’t quickly find a price for liquid fish oil, but flaxseed oil capsules  are at least 50% more expensive per mg than fish oil capsules  of the same brand. So, flaxseed oil doesn’t seem to have a price advantage.
However, flaxseed oil has a high omega-3 fatty acid content (and ratio to omega-6 fatty acids) and would be vegan. Another option could be to use powdered flax seeds. These are cheaper and have approximately the same fat content and profile, but are not in liquid form and would necessarily include additional nutrients and fiber. Because they are dry, they would also keep longer. However, I’m not aware of the extent to which Soylent relies on liquid oil for texture or nutrient uptake, so that might be a trade-off.