In the first... 40 years, or so, there's going to be a few main types of people who will give up traditional food for nutrition-complete beverages (which means Soylent and any further competitor that serves a similar product - all of these, from now on, will be referred as soylent - no capital refers to the class of food item, with a capital refers to the specific brand) - people who are especially busy will take it up because of the speed of it (I mean - a lot of them already take the vitamin supplement drinks like Boost, and this is literally a meal in a bottle). The "green" people may also start consuming it because of how low of a footprint it has on the environment. Vegetarian and vegan may use it as a complement or replacement - since it's a vegan, complete food source and all. There's also, most likely, some dieters who are going to take up on it - because by knowing exactly how much nutrition there's in a bottle, it's hard to over-consume. And finally, there's going to be the people for whom the product was first designed - the people who see eating just as a hassle, a time loss. People who don't enjoy eating.
After 40 years, soylent will be generalized enough that nutrition groups will start doing information campaigns, which will open it up to more layman-people who will try it and may convert to it because of it's simplicity.
And then, in 60-80 years, traditional food will be reserved for the elite - for those who have the time and money to buy real ingredients, because the middle class will be too busy working to eat traditional food, and the lower-class people be simply too poor to afford it.
That is, at least, my insight on why Soylent is the start of something. That, of course, applies only to developed countries - countries in development or undeveloped will have a much different path (I personally foresee very little impact on countries in development unless they make their own brand (which I think will not bode well for China), and it will become an outstandingly common assistance item in undeveloped countries - why send rice and other unperishables when you can send bottles of nutrition-complete, clean drink that have a shelf life, without any means of external preservation, of one year (and potentially a powder and water filters that would extend the life of the product for four more years)).