It's not clear to me why it even needs to be treated as a special case. In particular, the biggest other example of a language that has this "return or hanging

It's not clear to me why it even needs to be treated as a special case. In particular, the biggest other example of a language that has this "return or hanging last expr" I'm aware of is ruby, where the problem with it is that accidentally returning a value from a block might affect escape analysis for GC, but rust doesn't have that problem. In your example, the if is in expression position, so it's fine if it treats its bodies as expressions. I'm definitely not saying I want to pepper my code with returns, I'm just unconvinced semicolons help with avoiding that.