I just don't see any drawback for people (other than the actual modder who do it) to begin modding before the GECK is released. If their mod get broken by an update, it's on them. If the mod becomes a part of the game core, it's on them too. If, finally, a better mod is released when the GECK comes out, it just means that their mod they worked for will be forgotten. So what's the problem ? It doesn't actually hurt anyone. Hell, xEdit is a better tool than the GECK for a lot of applications, particularly batch-editing, comparing different forms, and conflict resolution (which the GECK doesn't cover at all).