You could already experiment with this today, in multiple ways. The most obvious would be to add a method (e.g.
.flip()) yourself, via an extension trait. You could then make an argument for why that method is not only useful but so incredibly useful it needs to have a one-character unary operator (as well as whether it fits the semantics of that operator). As a hint, such an argument would start with "a massive number of crates are using this, or contain a code pattern that would benefit from this"; that's the threshold such a proposal would need to meet, at a minimum.
You could also experiment with the syntax you propose using a macro, or a different Result type, and then use that to make a similarly compelling argument.
We almost never jump directly to "this needs short native syntax". Important steps that come before that: "does this need any native syntax", "could this be done in a library", "could this be done in a macro", "what's the most idiomatic way to write this today", "should this be done at all".