Originally Posted by Valloric
It's just something you'd expect of an ebook editor, now wouldn't you?
I personally feel that depends on whether your intention is to create a multi-format editor, or an epub editor.
In the former case, you'd expect the editor not only to read, but also to write, multiple formats; in the latter case, there's a valid argument to the effect that the application's task is to edit a specified format.
Mind you, if are planning to build a multi-format editor, it would be one hell of a valuable tool.