"This would mean, for instance, that the PC will not end up on a lifeless demiplane unless the players have somehow put that at stake via their play" seems to restrict the DM to things the players mentioned first, so while there might be something going on on the GM side, it cannot do so without explicit player decision / permission
Let me repeat a fragment of an example from
upthread, post 581:
When the PCs step through the portal from their resting place to the top of the tower, they find that it is not where they left it - on the disintegrating 66th layer of the Abyss - but rather in the palace of Yan-C-Bin on the Elemental Chaos. This brought the PCs, and especially the chaos sorcerer, into discussion with the djinni who had retaken possession of the tower and were repurposing it for the coming Dusk War. Mechanically, this situation was resolved as a skill challenge.
Sirrajadt, the leader of the djinni, explained that the djinni were finally breaking free of the imprisonment they had suffered after fighting for their freedom the last time (ie with the primordials against the gods in the Dawn War), and were not going to be re-imprisoned or bound within the Lattice of Heaven, and hence were gearing up to fight again in the Dusk War. He further explained that only Yan-C-Bin (Prince of Evil Air Elementals) and the Elder Elemental Eye could lead them to victory in the Dusk War.
The PCs both asserted their power (eg the paladin pointed out that the reason the djinni have been released from their prisons is because the PCs killed Torog, the god of imprisonment), and denied the necessity for a coming Dusk War, denouncing warmongers on both sides (especially the Elder Elemental Eye, whom Sirrajadt was stating was the only being who could guarantee the Djinni their freedom) and announcing themselves as a "third way", committed to balancing the chaos against the heavens and ensuring the endurance of the mortal world.
Sirrajadt was insisting that the PCs accompany him to meet Yan-C-Bin, declaring that mercy would be shown to all but the sorcerer. (The reason for this is that the chaos sorcerer - who is a Primordial Adept and Resurgent Primordial - has long been a servant of Chan, the Queen of Good Air Elementals, who sided with the gods during the Dawn War and is resolutely opposed to the Prince of Evil Air Elementals; hence the sorcerer is a sworn enemy of Yan-C-Bin.)
Things at stake in this episode of play:
*The PCs' access to, and ownership of, their Thundercloud Tower;
*Whether or not the PCs - especially the Sorcerer who is a servant of Chan, Queen of Good Air Elementals - will be punished (or similar) by Yan-C-Bin;
*Whether or not the Djinn will be able to regain the freedom they enjoyed before the Dawn War, or whether they may become even more imprisoned;
*Whether a Dusk War is coming.
The players did not give
explicit permission about any of this. That would (in my view) a boring and emotionally very flat way to approach RPGing.
What the players did was to establish and portray their PCs, and thereby signal goals and aspirations for their PCs, which I - the GM - used to establish framing and narration.
For instance:
*The players declared that they were teleporting back to their Thundercloud Tower, because they needed it to confront the Tarrasque;
*The Thundercloud Tower had first been introduced into play when the player of the sorcerer PC put it on an item wishlist, and the sorcerer PC found the Tower abandoned in the Glacial Rift of the Frost Giant Jarl (details
here);
*The same player had quite some time ago (in the play of the campaign) established that the sorcerer serves Chan, and hence is an enemy of Yan-C-Bin;
*In a recent previous session, a different PC had taken on the mantle of god of imprisonment, which has become "vacant" after the PCs killed Torog - this was the player's choice, made in response to an offer I put to him when he was in a somewhat desperate fight against Kas (details
here);
*The players, as their PCs, had been debating for a long time what their attitude was towards the cosmic struggle between order and chaos, and the possibility of a coming Dusk War.
The first two things are what put the Tower, and the PCs' access to and ownership of it, at stake. The second and third are what put a possible claim by Yan-C-Binn and the Djinn over the Tower at stake, reinforced by the fourth (given that, in 4e, the Djinn are an imprisoned people seeking their freedom). The third is what put the Sorcerer's freedom in dealing with Djinn and Yan-C-Bin, in particular, at stake. The fifth is what put the whole framing in terms of the Dusk War at stake.
This is an elaboration of why, upthread, I described this as high player agency play of D&D.
the highlighted part is why I say your GM has no agency, it all is decided by the players (and the rules). I am not really sure why a GM is needed in your vision at all.
I've repeatedly talked about the GM's role in framing, and in establishing consequences. Who do you propose is going to do that, if not the GM?