Q passive change, to go along with his lore and soul stealing blah blah blah. Makes him in his neutered form interesting, but not game breaking. Penalizes greedy enemy players and gives him a little more utility. Instead of him just gaining AP, make the opposing champion permanently lose that AP.
"Whenever Veigar kills a champion from ANY source of damage, he gains 1/2/3/4/5 AP and they lose 1/2/3/4/5 AP permanently.
No. That makes Veigar getting ahead do more then just power him up (via his passive AP, free farm for a while, and bonus gold + xp and maybe an objective or roaming), it ACTIVELY PUTS THEM BEHIND. That makes a behind Veigar still meh (whoops, I lost 5 AP. Good thing I have 400!) and an ahead Veigar frustrating as heck via a passive you can't fight at all (well, I just lost another 5 AP. Now that's 40. Good thing I don't rely on my scalings to do anything :( ).
Otherwise, there would be the bug problems of what happens if you don't have any AP (Do you get negative AP? Do your AP scaling skills now do less until they eventually do negative damage?) and how it interacts with items (okay, he just took 20 AP. My only item was a doran's Ring...so if I sell and rebuy it do I get my AP back?). Overall though, it's a frustrating, unfun mechanic that Veigar won't notice and that enemy mid laners won't notice unless they get behind, in which case they are going to acutely notice losing what little damage they do have.
