There was a delta wing version built over 20 years ago. IIRC, it performed superbly but for unknown reasons (probably part politics and part the generals not wanting it) the military never bought it.
The Chinese and who knows who else likely has all the engineering, either from buying it from Clinton/Gore or having it given to them by obama, if they haven't just taken it by any open door they might have found.
Given the fleet of F-16s around the world today and the retrofit/upgrade market potential well into the future, not to mention a few home grown look a likes, I bet the XL will fly again, one way or another.