Assuming his Q and R remain targetable abilities, "moving around and dodging everything" pretty much amounts to dodging his W. Assuming you build tenacity against veigar, even if he hits you perfectly with the stun it won't be an automatic hit until level 8 or 10, depending on when he gets his 3rd rank in E. The mana cost of the combo is expensive and he gets punished very hard for having his stun down.
What I think riot is trying to do:
Give additional counterplay to the stun --> all-in combo from veigar.
What I think is actually going to happen with those changes:
Mobility champs will get another strong matchup, this time against someone with mainly point + click damage. Neat. :|
Bad stuff (in my humble opinion) about it:
The counterplay to veigar (mostly) isn't in dodging his stuff, it's in itemization. In lane, prioritizing magic pen builds over pure AP builds (like
which gives you hp, additional utility, and reduces his R scaling from your AP), getting some tenacity, or getting some MR. If he can't evaporate you, he's in big trouble because his burst is insanely high but his DPS isn't very good and he has no mobility. I don't see what's wrong with that kind of counterplay. If you're an adc, you'll want
or
or
or a support with
... So what if you're "forced" into getting those? Buy them and his effectiveness drops DRASTICALLY. He has to be pretty close to one shot someone, and he only gets to one shot one person. The changes riot is making are in response to a "problem" that stems from frustration when Veigar goes on the offensive, and, in response, they're strongly affecting his defensive potential vs mobility creep empowered champions. Furthermore, the stun is very short range as it is now. It's extremely powerful in teamfights; in fact, it's all he's got for a teamfight after he uses his burst. Veigar wants to blow up one target; if he used his E on that target, he's now useless, and if he didn't, then he gets one E to influence the teamfight. It's got a fairly short cast range so trying to get a good one brings him pretty close to the front line and makes him stick his neck out. I think it's a fair tradeoff, and having larger-than-average teamfight presence is OK if you're on the losing side of a lot of lane matchups and sacrifice early game map presence because of it. Giving it an additional range, lower CD, and reduced mana cost may make it easier to avoid, but it's also going to let him do it from safety and possibly more than once. I don't think that's the right tradeoff. #soapbox
Good stuff (imho) about it:
If you have godlike reflexes and accuracy you won't be able to use it to immediately reset any bad situation you get in. I think powerful abilities like that should have to be used in a proactive, not reactive way, in order to be healthy for the game.
Now that that's out of the way, here's my opinion to your specific question.
What I think you're trying to do:
Give him back some of the offensive relevance of his E in 1v1 scenarios (be they in lane or small midgame skirmishes).
What I think would actually happen with that change:
Make mobility mandatory against veigar. As it is now, if he can land the stun perfectly it doesn't matter how mobile you are, but if he botches it and you're stuck inside or out you can at least avoid the W damage regardless of your champion's mobility. If there's an AOE slow, he doesn't have to try to land it on an edge he can just plop it right on your head, land the W, and run away while you can't follow because of the stun-wall... unless you can dash out through the slow.
Slows don't punish champions with dashes very hard; I always thought event horizon was an interesting ability because even if you "miss," it represents an obstacle for most high mobility champions. Granted since I think that mild "mobility creep immunity" is going to disappear with Riot's proposed changes as well, I can't really fault your idea, even if I don't like that part of it. It's also starting to sound a lot like an ability from another champion... 