Is it planned to introduce some basic economy that would make civs choose what to buy and sell based on what they need and provide a steady growth? Can the game track all the goods in the world at least rudimentary?
Personally I find this idea interesting - http://www.bay12forums.com/smf/index.php?topic=163691.0
Yes. Should be in the dev notes somewhere. But basically it's up next after mythgen and starting scenarios (politics and society) arcs. But maybe boats will come first.
So probably about 10 years from now, at least.
And it probably won't be 'basic'...
That idea described in "suggestions" is interesting because it could provide some basic elements first, elements that should be enough to make the world believable and realistic, without devoting that much time. I'm no professional programmer but perhaps Toady could provide something like described in that post while working on some other things before overhauling the economy entirely and making it very realistic, which seems to be the goal.
Why waste time on a placeholder when it's already planned? Just extends development for no real reason. There's a good chance that society and law updates will make any temporary system you put in now mostly obsolete. That's a year of work that gets thrown away.
Sure, I know nothing, but it's kind of hard to see Toady building up the motivation to do that when there's intersting things that still need developing (magic, boats, editor, etc). He's more likely just to work on economics simulations in his side projects until he gets somewhere near where he want df to be.
Such a placeholder could make the game feel realistic for the time being. Creating a proper economic system would be a chore and could well be the single most difficult thing to do to make DF a realistic world sim. Something along the lines I suggested would IMHO make the world more believable and its progression would make more sense.
When it comes to a real economy, just think how many things would need to be modeled:
1. Every single item would need to be present and tracked to really simulate trade, along with its supply and demand properly.
2. Entities would really need to appraise the value of an item according to their own needs. This might be tricky to do, but with a complex value/belief system of each character in the game it might not be that hard. Several examples:
2.1 If I need food and I have something of value, I am willing to sell it cheaper than I otherwise would. What's more, I will value it even less after some time when I'm starving and I would value it at almost nothing if I'm nearly dying.
2.2 Individual attachment can make a simple thing very valuable to a certain individual. An old shield with the coat of arms of an old kingdom might mean the world to a sentimental person who has once fought in its armies.
2.3 Even if an item is not in high demand in town A, it would have a higher value to a clever merchant who would try to purchase a lot of it.
2.4 A cunning merchant might make someone love an item they would otherwise not really want by using their emotions and making them value it a lot. Basically, as salespeople always say, you're not exactly selling an item, you're selling an emotion - like when selling someone a house, you make him fall in love with it by making him for example imagine how his kids would play there in the future. That's selling, and the real value doesn't even have to have much to do with it.
3. When it comes to resources, their price as it reflects the ratio of their usefulness/scarcity, would create a complex system of what materials are being used. If titanium is common, no one would keep using iron anymore. Also, entities that value their work more than combat should use their best materials to make tools first, unless they are threatened by another civ, in which case they will certainly need weapons and armor in the foreseeable future, which would make them value their weapons and armors more than tools, despite their beliefs.
4. The quality of goods could require a complex system. The quality of goods produced by each individual must be influenced by his civ's values, certain traditions, tracked inventions, perhaps the knowledge level of certain guilds, civ's attitude to knowledge and books which contain info on how to produce things, and finally on individual's characteristics and whether he had access to a mentor or not.
5. Usefulness of an item must be carefully tracked so that craftsdwarves know what to manufacture first. It is obvious that they will have to produce more farming tools than arms in the time of peace at least and civs' rulers might try to force them to stop producing everything but the most essential civil equipment and use contracts to buy a lot of arms.
6. The items must wear down so there is a need to replace them, and this needs to be tracked too.
7. Basically the game needs a complex system of contracts that make an individual want to produce a lot of expensive items as he expects payment. Also, how much an individual or civ ordering something can be trusted must be tracked too. Also, we need courts to resolve disputes which must happen, even if only because of the player not paying the craftsman.
Just my two cents on the issue. The world will never be complete without simulating those things, and those might not be that easy to simulate. If, however, Toady One manages to do all that, he will certainly be the first person in history to create such a complex and realistic system and who knows, maybe even economists would use it.