Veigar has been interesting ever since his rework a while back. I do understand that his stun lacked counterplay. However, his kit seems to lack cohesiveness now. He has no way to set up his stun, and his stun is required in order to land W.
Other mages have ways to land their CC, or they have easier to land CC. Vel'Koz slows with Q and follows up with E. Morgana can ult, and then land the binding either while they are slowed, or right after the ult root. Xerath, if needed, can land his slow before his stun. Ahri has a pretty fast Charm, that can be hard to dodge.
There are more obviously. But it just feels like Veigar has no way to land his stun on a competent player.
So I was thinking, what if his Q slowed you? And the slow amount could scale with AP?
For example, it could always slow by 20% for 1 second, but it could gain an additional 10% slow for every 100 AP you had. Numbers could be changed. So, at 500 AP, you'd slow for 70% with your Q.
This would solidify his late game playstyle, but it would give him a way to land his cage while they were slowed by himself. However, he wouldn't easily be able to do this early game due to lower AP.
Another idea could be to make it so enemies could get slowed by Veigar while trapped inside his cage, but only if he hit them with an ability first.
For example, Veigar could trap an enemy inside E, land Q for the slow, and follow up with W.
Or, he could trap them with E, ult them for a guaranteed slow, and then W Q them.
If this went through, I'd be fine with a range nerf on his E, or even a cooldown nerf, or both.