I think just removing his mana would be problematic, because yeah, he'd be in poke heaven.
That being said, though, I really do think his problem is that his current mana costs force him to be extremely defensive against other champs he's like to lane against (Shen and Riven come to mind, especially), and even just using his Q to farm causes him to run out relatively quickly. In the interest of making him actually usable again, I think it might be in Riot's best interest to decide whether or not they want him to be a brusier or a carry; either make his Q more mana friendly, but less physically powerful (so he can farm reliably but can't use it to poke so hard early-game), or make his whole skillset a bit "tougher" early on so he can at least stand toe-to-toe with more popular bruisers.