That's exactly where it would be going
if a market economy makes its way into the game. The farmers, fishers, and butchers produce food, the cooks process and preserve the food, and the food stores sell the food. As prepared meals would be more valuable and more desirable, your food economy will benefit from having it available as long as your dwarfs can afford it. (If your fortress is some poor crap-sack you might want to keep your cooks busy just preserving food instead.) That means your food folks walk away with more money and buy more crap from your other merchants, which means they walk away with more money and buy more crap too. Otherwise, this would just be another way to keep your cooks employed and busy under the current rudimentary economy system, not that they'd have a lack of work anyway because of the food preserving they'd probably be doing. (To be honest, they're pretty worthless
already because you don't actually have to cook a damn thing, and the alcohol-to-food exploit for newbies was the only thing that made them valuable before. Making them necessary through food preservation and then giving them an economic incentive to cook if you so chose would make them more dynamic and broadly useful as laborers. Of course, with stoves, you might only need cooks to preserve food, and possibly prepare food for nobles or something odd like that.)
With the food shop dynamic taken into account:
- A dwarf that can afford to buy prepared food would prefer not to cook for themselves and will be happier because of it. (They'll eat quicker because they won't spend time preparing the meal, too.) Kitchen produced goodies will tend to be much better for reasons listed below, giving stronger happy thoughts.
- A dwarf that can't afford the cooked food item but can afford ingredients will take the time to do so if they have access to a stove. They enjoy a cooked meal but without the happiness causing perk of having it made for them by someone else. (Kitchens could have access to certain ingredients that can't otherwise be used at home, and a home stove could only produce a simple meal. Your store-bought foodstuffs are going to be at least as good as what's being made at home, and will most probably be much better.)
- Poor dwarfs or dwarfs that don't have access to cooking facilities of their own will eat the stuff uncooked, and may get an unhappy thought from the poor quality of their food.
An alternative approach to this whole idea would be to make it so prepared meals are consumed on the spot and never stockpiled. A kind of food shop could prepare food for paying customers as they approach, one serving at a time, and do so using whatever raw and preserved foods and other additives are available. (The kitchen workshop as we know it would retain its fat rendering and food preservation duties, but food preparation would be delegated to this wacky food store thing.) The above logic of preference remains the same; a dwarf that can afford it will more often than not have someone else prepare their food, and will receive undoubtedly better food. The rest have to suck it up and cook it themselves if they can, possibly around a community campfire of some kind, and won't have it so good. If quality bias or even customer exclusivity could be assigned to one of the above food shops, you could have an especially fine one set aside for your nobles and special guests, too.
Of course, maybe they don't have a culture of hospitality. Maybe they could all just eat at home, without any restaurants. (Cough, dining hall, cough.)