I've been playing new Veigar 24/7, and this is what I think he needs
His Q is so unreliable when it comes to hitting enemy champions, which he absolutely needs now in order to burst people due to his ult nerf.
My suggestions? Any buff works, really.
The best one would be either widening the hit box or making it do more damage because its damage seems pretty weak despite being a hard to hit skill shot.
tl;dr Him not being able to land Q is his only problem now, unless riot buffs his W or something