Currently, HA10 gives you one a 5% chance at a non-S1 5* hero when putting in a single 5* hero (most of us use only S1 heroes). What if we were allowed to add more than 1 hero. 2x 5* gave you a 10% chance, 3x - 15%, 4x - 20% and so on. It would give US something extra, without breaking the game economy.
I apologize if someone has offered this idea up before. Mods, feel free to remove or merge as necessary.