I have been using a similar solution to what IBLocalizable does for quite some time using user defined attributes, although not having to define user defined attributes myself is admittedly so much cooler!

Over time, I realized that I was creating outlets just so I can capitalize or uppercase the localizable properties of UI elements, so I added a few extra methods for handling that. Something like:

func setLocalizedUppercaseText(_ text: String) {
    text = NSLocalizedString(text, comment: "").uppercased(with: Locale.current)
}

Do you think something like that, implemented according to IBLocalizable's architecture would make sense to be added?