Uitë:
This would require a re-structuring of what mods are allowed on what items, and seems like it would be unintuitive.
Tell the player that two agility mods and a tech mod combined in any way will give them a sniper mod pack, OR
Tell the player that modding their pistol 2A1T will make their pistol sniper modded, and thus they can't without WK.
4B won't fit on an armor... in fact, 2B won't. And, on the way to your Onyx-packed armor, you would likely at some point wind up with 400% 6/6 red armor, which is a little silly; and if you could do that, why not do 4P1B armor, and of course, as things are now these would require WK2.
I back requiring WK to make uniques, but only one level. This idea is meant to proliferate assemblies and be able to count on exotics and maybe a unique appearing, not to force WK2 for any game that wants a chance at one of the neatest toys, like it does now anyway. Master assemblies and ridiculous T3SF plasma rifles are your reward for spending the extra level, and if this suggestion warrants serious consideration, it might encourage some assembly migration, limiting the number of basics and increasing the advanced/master pools in the course of balancing.