There's been a bunch of post about reference movies lately. This is definitely an advanced workflow tool that requires a buttoned down workflow to work reliably. The benefits are huge both in speed and storage savings.
Unfortunately Apple has not included ref move export in FCPX. The reason for this is because FCP relies on QT's replacement AVFoundation which currently does not support ref movie creation.
If you value QT ref movies in your workflow or product (hint hint Squarebox) please tell Apple that ref movies are important and to please add it to AV Foundation.
AV Foundation is under the OS team at Apple so the OS Feedback page is the place to request ref movie support. FCPX has a built in feedback feature.