I've noticed it's really annoying playing laning phase against a Xerath. If he charges his Q, the only smart thing to do in most situations is to back off & try to dodge. Trying to engage on Xerath always results in him ending the charge on his Q immediately, hitting you in the face for full damage, running away, and then using E if you try to chase more. This especially annoying for short-ranged mages like Mordekaiser, Ryze, and Vladimir. At least when facing Lux and Nidalee you can hide behind minions, but against Xerath, there's nothing to do but run away, abandoning your farm.
What if the longer Xerath charged his Q, the more damage it dealt? If he was rewarded for taking the risk of charging it longer and penalized for always being a coward, he'd leave a lot more room open for counter-play.
And hey, if rather than having charging his Q increase its damage, it gave the spell increasing amounts of Magic Pen, Xerath would keep the artillery feel of his Live version. And, it would mean that short-ranged mages (Morde, Ryze, Vlad), who tend to have lots of MR wouldn't get too much of an advantage against him.
What do you think?