I mostly enjoyed the crafting system in DA:I, but I thought it was problematic for armor because the armor appearance was tied in to what stuff you could get ON the armor, so wearing an appearance you liked was often restricted to eating some minor or major stat penalties. That's no good, particularly considering how limited the appearance options were ANYWAY. And what's the point of buying an armor pack when the armor in it is only going to be good for a level or two because it's severely limited in its potential?
So, instead of that, I'd suggest doing something like this:
1. The number of pieces you can use for the "base" of the armor is dictated by your level (perhaps with some modifications from some sort of crafting investment system, like something you buy with the equivalent of Inquisition upgrades). So, if you're level 17, you can use 17 pieces to form the "base" of any armor.
2. Slots are 1/2 your level (plus modifications). The modifications would be better if they're more specific, like, "+2 to all leather slots" or similar.
3. Put in a system for swapping types of slots. Maybe have 1 "dedicated" slot that can't be swapped, but 2 that can be jiggered around a bit.
So, basically, you can use whatever armor appearance you like the most and they'll all be fairly similar in their basic attributes.
I like the general direction of this and the dedicated, or fixed vs. variable is how I would put it, slot idea a lot.
If we're dreaming up new systems that may be introduced in DA4, why not go all the way? Completely separate the look from the function of the armor. You can craft any look you want, but function is purchased separately. I dunno, maybe that's what you meant? I'm a bit fuzzy on how #1 and #2 work.
Say a light armor, for mages, comes in XP level graduated slot counts: from 2 to 8 or whatever. The capabilities of the armor (aside from just basic physical defense) come completely from features you craft to add to the slots. I'd prefer to leave the slots undifferentiated -- if I want a 6 slot armor to have nothing but offensive buffs, let me do that -- but as OP suggested, maybe for unique armors there are 1 or 2 fixed slots that always have the same feature in them, so that everyone with, for example, The Griffin Plate armor, always has total immunity to physical effects.
But even then, we should be able to override the fixed slot if we want. You can't pull the unique feature out and put it on something else. It would be more like a DAI rune, if you override it, it's gone. That way, if the armor look of a unique item is what we want most, but it has a stupid fixed buff, like Berserker or something like that, we can get rid of it.
Notice that this completely does away with Upgrades. You craft the look you want, body, arms, legs, helm. Then assign features to slots.