What if Nocturne's Q let him go through walls?
Basically, if the trail is within a wall, that portion of said wall becomes similar to the base gates and Azir's ultimate in that Nocturne and only Nocturne can walk in there. This would apply both when you just shoot the skillshot through it, as well as when an enemy is hit, then dashes over it. The way I see it, this would fit in with his spooky, haunting, chasing thematic of the champion by giving him even more sticking power, and possibly make him somewhat of a check pick champions like Tristana, Ekko and LeBlanc.
I know that he was just buffed and is actually decently strong IMO, but this is just kind of an idea I had. Maybe some kind of compromise between a long Ult range and this would be cool.