Well, yes. When I look at it though, there's actually 3 layers to this.
1. There's classic modding. 2. There are creation tools. 3. GM mode allows you to manage a gameplay session mostly in real time.
Yep, exactly. 1. Modding - should allow the hard-core to actual edit/create 3-D models, sounds, voice-overs, scripts, etc.
2. Adventure Creation Tools - should be easy enough for non 3-D modelers and non-scripters to create adventures that hopefully don't require a GM to moderate.
3. GM mode - needs to be easy (and powerful) enough for GMs to interact and adjust stories to the players choices. It should not need full on terrain editing, but should allow placement of "large" terrain related assets like giant boulders, or collapsed mine debris, etc. Basically easy access to any placeable "objects" including lights and sounds.