SomeView.swift

public protocol StoryItem {
  var id: Int64? { get }
}

public protocol TypeErasedRestorable : AnyObject {
  var typeErasedStoryItem: StoryItem? { get }
}

public protocol Restorable : TypeErasedRestorable {
  associatedtype T : StoryItem
  var storyItem: T? { get set }
}

extension Restorable {
  var typeErasedStoryItem: StoryItem? { storyItem }
}

public struct LabelItem: StoryItem {
  public var id: Int64?
  public var text: String?
}

public struct StickerItem: StoryItem {
  public var id: Int64?
  public var imageName: String?
}

class LabelView: UILabel, Restorable {
  var storyItem: LabelItem?
}

class StickerView: UIImageView, Restorable {
  var storyItem: StickerItem?
}

class SomeView: UIView {
  func foo() {
    let restorableSubviews = subviews.compactMap({$0 as? (TypeErasedRestorable & UIView)})
    print(restorableSubviews.map { $0.typeErasedStoryItem })
  }
}