When you add {{DISPLAYTITLE:}} to a page, in most cases you will use a label very similar to the name of the page (and with default configuration, you are even forced to do so). So instead of showing an empty input field, VE should prefill it with the title. Currently, you have to copy the title before you open the dialog (which in practice means: open the dialog, see that you can't copy the title while the dialog is open, close it, copy the title, open the dialog again), or type it in manually, which both is inefficient.