I'm not sure it's better enough to overcome the friction of __ already being a valid identifier. Hopefully there aren't too many people using things like mod __;, but they could be. And it feels a bit more like Stroustrup's Rule than necessarily a substantial difference.
If we're jumping to something other than leveraging the existing "_ means 'infer this type'" we have from things like Vec<_>, then I'd rather pick a different syntax entirely. For example, I've mentioned the Swift-inspired idea of let .{ x, y, .. } = foo(); or if let .V6(ip) = get_ip() before.