So this looks a lot like XAML[1] for WPF (Windows Presentation Foundation)[2] to me. and I'm actually quite surprised that this was not the case for iOS development from the beginning!
(declaimer: I never touched native iOS development before as a 100% Microsoft technologies professional)
XAML was definitely one of the inspirations for MarkupKit. It was also inspired in part by MXML (Apache Flex), FXML (JavaFX), and to some extent HTML. It's also conceptually similar to the markup language used to build Android applications, though I don't have much experience with that.