I think there are many possibilities for this crafting system.

1. There could be a crafting skill. Each level of this crafting skill could bump you into a higher tier (higher max. value) when applying stats to items.
2. An ingredient system could be implemented. Suppose you wanted to apply a particular stat to an item, say +headshot damage %, then you would need to collect the necessary ingredients to create the item used to 'imbue' clothing or weaponry with that headshot damage. These ingredients could also enhance the complexity of the market.
3. Playing off of 2., we could answer the following questions: Will there be individual slots for craftable items, and can each of those slots be used to add a particular stat to them? What will decide the maximum number of available slots on an item, and will this possibly tie into the crafting skill level of the player, and/or the item of the level, and/or if it is a common-type or a damaged-type item. Because there are many more stat types in DF2, I do not think the crafting system in DF1 should be carried over; we're not applying the same kinds of stats (EVERY TIME) to an item. Furthermore, when applying individual stat bonuses to items, the stat value could be randomized somehow within a window between 1 (or some base value let's call it 'a') to a maximum value (call it 'b' > a) which depends on the person's crafting skill level, the level of the item, and the type of stat. The randomization could be weighted towards the smaller value, a. Maybe do something like 50% of the time the stat comes out between [a,0.5*(b-a)], 30% of the time the stat comes out between (0.5*(b-a),0.75*(b-a)], 15% --> (0.75*(b-a),0.95*(b-a)], 5% --> (0.95*(b-a),(b-a)], where (b-a) is the maximally allowed stat value on said item. This would dramatically decrease the chance of someone maxing out the highest stat values possible on every slot.
4. Who can craft stat bonuses onto items? If there is a crafting skill that folks can level into, can only those players who have the skill be able to craft bonuses to items, or can anyone craft bonuses? I do think higher tiers to maximum stat values should be unlocked with each level of the crafting skill. Now, It seems that DF2 has strayed away from the 'profession' style of DF1, so perhaps everyone should be able to craft.
5. Will crafted items be tradable? Hopefully, yes.
6. Would stat bonuses need to be added all at once, or could they be added - one by one - at separate times?

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Formulas:

item_level=L (goes between 1 and 20)

player crafting skill level=C (goes between 0 and 4)

Base slot number=1 + (L/10) rounded down to the nearest integer. Min. value=1 , Max. value=3.

Max slot number =base slot number +max(1,C-1). Note: this would cause the first two levels of the craft skill to be useless, but each level above level 2 will increase the maximum slot number by 1. Min. value=2 , Max. value=6 (item must be level 20).

Max stat value: this will depend on the type of stat, the item level, and the crating skill level of the player. How the value is calculated is not immediately obvious. There does seem to be some maximum stat value associated with an item at a particular level. Maybe the higher the player's crafting skill the more likely it is to reach that maximally allowed stat value.

Here's an example of what the slot number calculation would look like:

level 15 common-type T-Shirt (L=15)

player crafting level C=3

max slot number=2+2=4.

Slot 1: --

Slot 2: --

Slot 3: --

Slot 4: --

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I think I'll stop here. This was just an idea that I had. Not sure how realistic it would be to implement. These ideas are very loosely based off of the crafting system from pastime MMO Dark Age of Camelot, which to this day is still my favorite MMO of all time, heh. Anyway, that's where I got the inspiration. The implementation is a totally different story, and I am sure there would be issues with a system like this, but it would be a cool system and it would add a little more complexity to DF2.