Why do you think it's specialized to this specific case, I understand my file-upload component could be used anywhere where file upload required you only need to supply your specific on<del>u</del>Upload handler and will work.
I don't see the point in extending the [TextField](https://github.com/emberjs/ember.js/blob/v1.5.0/packages/ember-handlebars/lib/controls/text_field.js#L30) since it's really just a thin extension of the `Ember.Component` with a few text input specific stuff, and the file upload is not even a textual input so it wouldn't make sense from my point of view.