Sorry, but top lane variety should not come at the cost of inherently breaking the lane...
As much as I enjoy facing a Hecarim with Skirmisher's Sabre, him using Smite on me shouldn't let him deal physical damage, magic damage, and true damage all at the same time whilst I deal 20% less damage to him.
Take note that I'm simply using Hecarim as an example; Smite yielding egregious power to a select group of champions in a place it shouldn't is the concern.