Bethesda's recent editors act sort of like legos - you are provided with pre-made building blocks and you can configure them as you like. I'd assume the RAGE editor is a full 3D editor, where you design and texture everything yourself rather than using pre-made units.
But this is just speculation on my part. The presence of mega-textures already changes things about, perhaps they'll do something more like the GECK and CK.
Have you seen the editor preview pics ? Starts some minutes in http://www.youtube.com/watch?v=2USBm4hMOAw
It is going to be pretty big stuff, it may challenge the tools Unreal puts out for UE3 (not necessairly UDK, these mod tools won't be free version of an engine)
I really like the fact carmack doesn't want to go into licensing wars, EPIC was doing it for a long time and see what they made, a crappy dudebro console game, crytek has stepped in and they made the biggest most utterly screwd up consolized PC port with modern warfail COD crappy x360 15 year old kid gameplay and stuffed into a "PC" version, that was Crysis 2. The biggest failure of 2011, a shame and a disaster, like an insult to the gaming community.
If they told more about the VR stuff they were doing, we might get something to be busy with so rage mod tools would be easier to wait for, yes he made updates, but nobody really had a clear idea.