Well, it would be nice to see weaponry evolution start with world generation, or shortly after, but it also might be fun if the game began with the dwarf "steel age", or shortly after steel is invented, since they're the only ones using it. That way, you might see a lot of different weapons, in other materials, but you'd be able to witness the complete evolution of steel weaponry.
Not that it would all be going on in your Fortress alone: You might start seeing more interesting designs coming from the Mountainhome, giving you more trade options, and in a roundabout way, more player options via imports.
As far as implementation, I think it would be best handled with a deep set of random lists for the computer to select from, with the items on the list (barbed, smooth, wavy, serrated, whatever) trended from the dwarf's personality, skill level, cultural and other factors, but based off of compatible designs and (when possible) real-world examples.
Each dwarf weaponsmith could then work from a narrow (but still somewhat varied, for the sake of interest), range of possibilities.
Probably, this would best be handled by ToadyOne creating the basic structure, and then giving us the tools to mod it properly.
As far as how the comp would know what to produce: I really like Aquillon's suggestion of style based on the dwarf's personality. So the comp wouldn't really know, but you as a player could choose to have one dwarf making all your spears, for example, and another, say, making all your swords.
Whichever one you liked the best, you'd use the most, giving more and more examples of that weapon style, which possibly students might be able to learn from.
This is historically fairly realistic. Weaponsmiths often tended to produce in a limited range.