UIFont+MonospacedDigits

extension UIFont {
    
    static func monospacedDigitsSystemFontOfSize(fontSize: CGFloat, weight: CGFloat) -> UIFont {
        
        let originalFontDescriptor = UIFont.systemFontOfSize(fontSize, weight: weight).fontDescriptor()
        
        let fontDescriptorFeatureSettings = [
            [
                UIFontFeatureTypeIdentifierKey: kNumberSpacingType,
                UIFontFeatureSelectorIdentifierKey: kMonospacedNumbersSelector
            ]
        ]
        
        let fontDescriptorAttributes = [UIFontDescriptorFeatureSettingsAttribute: fontDescriptorFeatureSettings]
        let fontDescriptor = originalFontDescriptor.fontDescriptorByAddingAttributes(fontDescriptorAttributes)
        
        return UIFont(descriptor: fontDescriptor, size: 0)
    }
    
}

Ah, you are right. They seem to have fixed this with beta 4! Great to know. 👍