No file upload in action

I want a user to be able to provide a file in an action, but this seems impossible. Therefore I decided to use a command. This solved the problem, but why is it not possible to use file upload in an action?
Code example:

	'Files': collection ['File name'] {
		'File name': text
		'File': file
	'Upload file': command { // <-- Action not allowed...
		'File name': text
		'File to upload': file
	} => update .'Files' =
		create (
			'File name' = @ .'File name'
			'File' = @ .'File to upload' // <-- ...when using file property

As you said it is not possible in the language. But I can’t think of a reason why it should not be possible. @gjkunst could we support this in the language? I don’t know if it should be a ui scalar but at least a ui target.