It exists already.
SwiftUI to Jetpack Compose: https://skip.tools
And a less mature but very interesting project with a SwiftUI-like API for UI across macOS/Linux/Windows plus some emerging support for Android and even a TUI target contributed by Miguel de Icaza: https://swiftcrossui.dev
> It's a description language that system frameworks interpret and create NSViews and UIViews and CGLayers etc out of.
This is out of date. FYI parts of SwiftUI are "native" now. Notably the new Liquid Glass UI was written in "native" SwiftUI. UIKit and AppKit actually wrap SwiftUI views to render Liquid Glass now. Although SwiftUI-exclusive APIs have always existed, this was a notable step in a new direction and suggests the future of UIKit and AppKit is a unified "native" SwiftUI implementation.
They've also been ripping out UIKit/AppKit implementations of SwiftUI views... IIRC List is no longer a UITableView for instance (could be confusing with another component though).