I agree with above poster.
Beside the trouble of "choosing" who are advance players that are deserving to get the editor and who arn't, doing so would only limit your game's potential.
Who knows, the expansion may be played by some good map makers, but they would not have access cos they are not deemed advanced, unless there is some method of proving such self worth.
By releasing it to the public, those who are good and dedicated will prove themselves by the mods they make. The more moddable the game is, both in availability in the editor's comprehensiveness, the more impressive things may come out of it.
DotA, from warcraft 3 would be an example. Hmm, "DotA: Kings Bounty". I see a mod conversion.
