I think if you want immediate impact on the modding scene, you have to make it open to make changes to the main game in many different ways. My understanding was you weren't able to change the main game, like add new NPC, baddies, landmarks etc. That is where Bethesda does it right, that is why you have mods day 1 and 100's in weeks. They aren't standalone mods, they are mods to the main game.
Well you can add new NPCs and objects and such, but you can't edit existing ones except their stat files. But you couldn't make them part of another quest or add loot tables to an existing NPC because the original data supersedes the mod data. Somewhat annoying and that'd be a nice fix to be able to edit existing content, but it doesn't interfere with adding new content.
