Hecarim Passive
I've seem issues with Hecarim lately, and part of it is indeed that his passive is bland and-outside of home guard shenanigans-not useful. I've got a simple suggestion in the form of a buff (and if it sends him over the top he can be nerfed in other places).
Warpath: Hecarim additionally gains Bonus Move Speed based on his Bonus Attack Damage. Kind of like Vladmir is the AP/HP guy, Hecarim could be the Movespeed-AD centaur. I'd recommend against letting them feed into each other like Vlad's does, but I think this would be a good idea overall, once balanced.