We already got AutoSmite integrated into GoS, but it still can be greatly improved by adding a simple (?) function - Spell enhancement. How would it work? It should force the champion to use one of his spells (or even full combo) and then instantly Smite the creature still during the last attack.
The use of such a mechanism would ensure securing the buff on [Smite DMG + Spells DMG] hp instead of just [Smite DMG]. The impact of such a mechanism would be most noticeable on Nunu due to his insane Q+Smite combo, since his Q exceeds the damage of the Smite itself.