I like your ideas although I have to say that this sounds like a game in itself aka way too complicated and work-intensive for DOS 2...
I agree, it is rather hard and expensive to put this ideas into practice. But it is only the first stage of gathering ideas, brainstorm. It is usually recomended to gather all ideas even absolutely crazy ones. Some of them can lead to real things.
GM mode should to be included in the main module of D:OS 2, or it won't be seen by most of players. It is obviously, GM can be like God in user's mods. But in the main module he should to have some limist (at least, during the first walkthrough). So I try to construct some examples. By the way, I think it is not too hard to give expirience to GM and open some editors options during game progress.
But when I dream on GM mode... Oh... Hereafter just a piece of my sweet dreams.
Click to reveal..
Just imagine, GM is a part of game narrative. It can repair the main pretension to GM mode - it has no value for singleplayer.
Imagine, there is some Mighty Thing linked with the player's characters. It grow stronger with players achievements. But it hates them, because its fate depends on such miserable creations... Oh, stop... I think, I just described The Transcendent One =D
Or may be some great mage soulbounded with players. And he tries get out from Hall of Echoes. Or it is an abomination which struck Source. The more often player use dark side of Source, the more stronger can Mighty Think interfer in players game. Or etc...
Ok, let's continue. Let's this Mighty Thing has its own story involved into players ones. If there is no GM in game session, Mighty Thing appears only in story and in random encounter (like it orginise attacks on player). It also can randomly increase strength of some monsters. If there is GM in game session, he can make the same and more. And he get his own story, which allows to see game narrative with different point of view. E.g., players think Mighty Thing want to kill them, But it just know they'll face with very strong enemy and try to prepare them. What does not kill us makes us stronger.