It's really about spicing up how the current plan system works.
You do have scope for playing with the stats on the end result by playing with the mats - but currently the plans are static with no variation apart from Quality which affects only the number of mats required.
OP plans aren't really any major change - the only difference is the use of an OP mat which limits the global availability of the number of items in the game- the end result is as predictable as all other plans.
So we already have changing the number of mats, which does affect the stats that can be achieved since you cannot have a 50-50 mix of seeds and nails if you are making basic or HQ jewels (for instance). The results are predictable (even with the advanced tools, they are predictable, just the chance of getting the result is not).
I submit to you that no crafter using high-rarity mats is going to use a plan that isn't predictable!
I think I understand what you are proposing now, learning a profession that allows you to (for instance) change the ratios of mats or add mats in a plan; changing HQ HA sleeves to take 12 wood, 10 resin 6 oil and 4 sap, instead of the current 10, 10, 6, 6. Or perhaps at higher levels the ability to add fiber/clothing to armor bits to put more mats into the plan. Have I interpreted your proposal correctly?
I don't see how you are going to make the mechanic so that the results are not capable of breaking the crafting game while making the results actually worth the effort of learning a whole new skill on top of crafting. Few enough people master crafting a few things, and even fewer master the recipes. Even those who have are often improvising the recipe when there aren't quite sufficient mats of the desired type/q/quality. This seems to me to be a major project in terms of effort by the devs, potential bugs and game balance issues, that will give a very few players something new to do.
In addition, how are you going to handle the models with this much variability? If a modified Fyros helmet continues to look like a Fyros helmet with only minor improvements in the stats, there's not going to be a big call for the new ones. (And if the stats are uber, then you've just broken part of the game.)
It's an interesting idea but I don't see it as likely to be implemented or implementable until Winchgate has a team of 20 devs and 5 modelers.
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Remembering Tyneetryk
Phaedreas Tears - 15 years old and first(*) of true neutral guilds in Atys.
(*) This statement is contested, but we are certainly the longest lasting.
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