In the SWGE forum someone was also saying that cast members had started offering shipping services and making it clearer where to go/how to go about that while you're still in the park. But yes, so far people have been reporting that they've been able to take them as carry-on--I'm guessing since it's so long and has to go in the overhead that it might count as your carry-on bag rather than your personal item. Not sure, but I'd personally avoid bringing anything else that wouldn't fit under the seat if I were carrying on a lightsaber, just in case.
I may be wrong; if someone else has done it and knows more, please chime in!