I did a little research and there IS a functioning mod called Blacklist by Furgl that allows you to set an item pick up blacklist. For example, you can put Cobblestone on your list, and then when you are mining your bag won't fill up with cobblestone that needs to be repurposed or disposed of. This might be something that could be attached to say, an ULT purchase or perhaps as a separately purchase-able command. Just a thought! (Also its because I am drowning in cobblestone haha)
This seems like a cool idea; however, right now we have no plans to add this feature. Thanks for suggesting!