I would prefer to see this implemented as a global function. That way, autocomplete does not get polluted, but developers that want and know about this optimization still have easy access.
func areKnownIdentical<T: KnownIdenticalComparable>(_ lhs: T, _ rhs: T) -> Bool
The main benefit is that this allows working with optionals, where there are overloads to areKnownIdentical with T? on either side. If both values are nil, return true. If only one is nil, return false. If both are non-nil, call protocol function (e.g. a.isKnownIdentical(to: b) or static areKnownIdentical on T).