I believe there will still be plenty of stuff to do in this release though. But the main quest for example will not be in. So it'll be more of a sandbox this time I guess.
They basically really wanted to get the custom content out (there is a lot of it) out to other builders and also present the mod in its current shape. I think they're also keen on recruiting more members to finish it.

EDIT: If you want to lighten the download a bit later when the actual mod is released, you can start downloading the excellent soundtrack now: http://nwvault.ign.com/View.php?view….Detail&id=718