are there any plans to add built-in components or macros for common UI patterns, like modals or form validation helpers
That sounds valid ideas. Since it's a simple template engine, I avoided adding many features like you mentioned. Maybe, if you want those features, you would love yew and leptos which are other UI frameworks with Rust.
https://github.com/yewstack/yew https://github.com/leptos-rs/leptos