SInce you need at least Elite Orbs to be able to craft a 4 star thing, to then be able to use the Eternal Orbs, a recipe to craft Eternal Orbs down to Elite Orbs would be helpful.
There is already someting like this for Fire Crystals.
You should be able to buy the recipe from a Vendor IMO, not get it in a mission.
Maybe a recipe to craft Advanced Orbs from Elite Orbs would be okay, too.
This would also be a chance to add the two currently useless minerals to the recipe. For example it could be 100 Crowns + 100 Monstone + 100 Valestone + 2 Eternal Orbs to craft one Elite Orb.
I remember when I asked to have this for radiants.
They put it in.
Two weeks later, drought.