User blog comment:LivesByProxy/Vision: Sight, Stealth, Detection, & Denial in LoL/@comment-24420226-20151014040602

I don't see the justification for Karthus' wall inhibiting vision. While it looks like - and is reffered to colloqually as - a wall, mechanically it is nothing near a piece of terrain. It's just line-shaped AoE effect that has a very small width (i'm not sure what the actually width of the effect is).

I'm bringing this up becuase it could be an abuse case. With Anivia's wall, you propose it would interrupt vision and thus render her untargetable to her opponent. However, casting her E would instantly reveal her (as casting targetted attacks and abilities from concelmeant always do), making her targettable again. It's still a buff, but maybe not completely abusive. However, Karthus does not have any targetted abilities. If Karthus gains concealment from his wall, he can freely attack enemies from behind it without revealing himself. This could make it difficult for opponents to retaliate against him without having to advance upon him. Minions also would not be able to target him, since they would lose vision if they are not already on the other side.