I support the idea.You could make it so that you can't cast IA while wearing the Vecna, i believe... Not sure if the fact you can't change your armour while fighting makes this a good idea. You can always claim that there are "strange fluctuactions" in your magic aura, that makes IA fizzle.
If you mean Aura Cleansing instead of IA, it's indeed possible.
Worth debating.
Opinions?
So do I. I never liked the fact that you can cast an unlimited number of spells with Aura Cleansing if you wear Robe of Vecna (and not only average spells, but also very powerful ones, like Finger of Death, Mordekainen Sword, Abi Dalzim or Incendiary Cloud).