The shader system should be converted to the same system that armor and weapon mods currently run on. When you get a shader for first time, it's permanently unlocked and in your inventory, When you want to apply it, you just pay a small amount of glimmer.
I don't think anyone enjoys the laborious task of deleting huge stacks of shaders. This has been a problem since early D2, and I think the new mod system is a good template to fix it.
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I have always been against the current shader system. There is no reason whatsoever that we need to keep purchasing the same thing we've unlocked over and over and over again. There are plenty of material and resource sinks in the game already. This is tedious and unnecessary.