While I'm not against this idea, I cant help to wonder where the QoL-aspect is?
Because you're right: You can repair any armor with Grade 7 Dark Matter, so thats all you need to carry around. The other six might take up storage space in the database, but they really, really dont need to take up your inventory space (as you pointed out yourself). So unless its really bugging you not to use the most optimal (aka cheapest, aka "on level") dark matter to repair your gear, the issue you attempt to solve can already be fixed. And if you're that deep into optimising that you carry around anything but Grade 7... well, you might have an entirely different problem in that case...