Customising the new CKEditor5 in Craft 3 How do you configure the new CKEditor editor to e.g. add images? Do you create a config/CKeditor folder with a .json file and install the @ckeditor/ckeditor5-image package?
I don't think so. You can see the entire code here

ClassicEditor
    .create(document.getElementById('{$nsId}'))
    .then(function(editor) {
        $(editor.element).closest('form').on('submit', function() {
        editor.updateEditorElement();
    });
})


This is the javascript that triggers the editor, as you can see, there are no config settings provided yet. I searched in the entire plugin but I could not find any other Javascript functions that are triggert so unless they provided a really nasty method to include them in the original editor js file you can't change them yet.

The only "configurations" are Html Purifier

Edit 

However - you could create a feature request or you could implement your own code to provide settings. You only need to change a few lines - it's totally trivial