Credit for this goes out to @AngelForge as it was their idea, I'm just posting it out in the hopes it gets noticed and passed onward.
When you pull a card from a pack that you already own AND is mastered, you get another draw of that card at that rarity level. Whatever the result of that extra draw is what you get. This has a twofold bonus. It gives a good reason to master cards and move up tiers. It also gives helping hand to the issue of receiving duplicates.
e.g. I pull Aetherworks Marvel from a Kaladesh pack, but I already own that and have it mastered. That card gets re-rolled @ mythic quality for another attempt. It re-rolls into Dynavolt Tower, which I also already have, but it does not get re-rolled again. So in the end I receive Dynavolt Tower.
It could be too onerous to do this for commons as well, so maybe just uncommon and above.