I disagree with regard to "logical." This is clearly a discussion about preferences. And for me "~>" is way too close to "->", and if the font makes it not look too similar, it also makes it not look like an arrow anymore.

Your theory about skimming it seems to be dependent on the previous developer doing everything right. What if ~> was used by accident? What if it's in the wrong place of the expression?

Thus, my personal preference is for "?->". I find it clearer, since it stands out more. This also has the advantage that somebody who doesn't know it doesn't just scan it as "->" and wonder why everything goes wonky. They see something that doesn't make sense to them immediately and have to look it up.