For my use cases having function types as structural and not requiring explicit naming is quite useful. Allowing only nominal function protocols to equatable would definitely decrease value of the feature, but we could live with that.
Also, I need support for generic function, which in this context, implies generic protocols, which Swift currently does not have. In combination with generic type alias syntax mentioned in Improving the UI of generics, this may work, but it adds even more boilerplate code:
typealias CollectionOf<T> = Collection where Self.Element == T
protocol Predicate: Hashable {
associatedtype Value
func callAsFunction(_ value: Value) -> Bool
}
typealias PredicateOf<T> = Predicate where Self.Value == T