I'd like a system where we could find weapon parts from random non engram enemy drops, like scopes and stablisers, ect which you can use to overright abilities on your guns and armour (one use per item). Then have a vendor who sells nothing, but you can give him an attachement which destroys it with no retern, but allows the vendor to produce a blueprint so you can make more. Making blueprints should be pricey, but not legendary material pricy. Enough that braking down an attachment feels like an investment, but not enough to encourage the hoarding of items for 'the perfect gun'. Exotic weapons cant be modified of course. This obviously would need locking in aspects of trading.