Well...I'd say that it need wings at the very least, and preferably an engine
Lack of registration or temporary registration on an experimental flight permit is not a problem - let's face it, your logbook, once certified as correct and true, will stand on its own. If I ever need proof beyond that of hours that I flew I can go back to the flight records of whatever organisation for which I was flying.
Let's face it...flying is flying. Logging is all about proving that you were actually there.