It seems to me that there are two main types of loot in the game, loot found lying around which is easily accessible to the player and the rarer loot which is barred by requiring a feat in order to claim (I'm presuming, unless these instances are just bugged slices). I think that there should be some kind of differentiation between these two types of treasure. This feat loot could be a better rarer kind of treasure. A treasure that you would spot on your travels and make a mental note to try and return to (this would also increase the Metroidvanian feel). At the moment, I feel no incentive to go back to these treasures as I'm presuming that they are not going to be any different to the ones I find just lying around. Indeed, I've never actually gone back to one of these treasures to test the theory.
The only thing required to make these changes is a different style of treasure box specifically for the feat loot and some specific improvements to this type of equipment. Let's keep this simple, let's say that this feat loot usually has twice the durability and is always single or double positive in terms of its effect. These changes alone would create a rarer more desirable kind of reward for the player.
Another thing you could do is to make feat loot a permanent-until-death kind of treasure, albeit with lower stats, something like max 20% primary attack boost.
In terms of feasibility, this seems doable. Fingers crossed that these feat barred treasures are already tagged differently in the code, though.
