Personally, the main reason I'm looking to build a GUI in Rust is because the rest of my code is in Rust and I want to have an interface for it is because I don

Personally, the main reason I'm looking to build a GUI in Rust is because the rest of my code is in Rust and I want to have an interface for it is because I don't want to write my own DSL to express it via command line arguments or file inputs and I don't want to have to start using multiple languages just to specify the input to or display the output of my program. I don't really care all that much about speed, I just want to use the language I'm already using for the other parts of the project. The point about extensible widgets is I think more along the lines that what most people need isn't a way to create new and better versions of <input type=T>, but rather ways to say "if I want to input something of type T, you need to display these inputs in this layout and you can combine them to make a new object of type T". In other words, GUIs should focus on composition rather than inheritance.