FWIW I don't see it as likely that Kotlin's "if x != nil makes the variable behave as it it's the wrapped type" would ever be accepted into Swift. It's just too out of keeping with how the language behaves elsewhere, and with one exception has no real benefit over what's proposed here. But it does have a big downside in that it encourages explicit use of nil comparison instead of unwrapping.
The one benefit – the ability to assign a value into the optional within the scope – can hopefully be addressed via some kind of mutating borrow syntax like if var &x in the future. This could also extend to not just optionals but any enum as well i.e. case var .success(&x): x += 1 // mutate value wrapped inside a Result.
(hypothetical syntax here to illustrate concept, we can bike shed this particular spelling some other time)