@Crazy Jerome , sorry, there was something else that got under my skin yesterday...
I looked around and found various meanings and uses of "simulationist". The 2 articles so far in the Simulationist Manifesto on rpg.net, and the followup comments, don't seem to insist on a purist conception of "simulationist". There's even a comment that any system, including 4E, can be simulationist but with difficulty. The term being inherently subjective, I thought that trying to differentiate between a purist/"true" simulationism vs "pretend" simulationism was mostly academic. I'm not at all offended in any way by the distinction, I just didn't find it useful colloquially.
But here, to use the label to differentiate between RQ/RM and other systems, then ok...
I don't think that WoTC will ever chase after the hardcore/niche "true" simulationist market. I had thought that a modular 5E might be tweaked from the default to deliver a simulacrum of "true" simulationism (as I tried to brainstorm upthread) but if you say that a RQ/RM player will always consider that a "pretend" simulationism that doesn't deliver their desired playstyle, then never mind that.
However, I think WoTC can or might seek the "pretend" simulationist market, because they had it pre-4E.
Also, I think that the 3.X/PF fans are not a monochrome group. Some segment is playing PF because WoTC did not deliver a 3.75E. Some segment wish that PF was more streamlined by not trying to be backwards-compatible with 3.X (that would include me). I think they'll never go to 4E, may never try a 4.5E, may dabble but never stick with a 4.5E, but a modular 5E maybe yes.
I do agree that only a minority of D&D players are looking for deep immersion from "pretend" simulation.
And yet, Rich Baker on Rule-of-Three column has recently made several references to rules that encourage or discourage immersion. So game designers and players are seeking it to some extent. I think 4E is trying to "dabble" in immersion, perhaps moreso now than before, and I think "Legends" would be the same, but I think "Lore" could do it better.
Perhaps my miscommunication was to conflate simulationism and exploratory/sandboxy (for me, they go hand-in-hand). In my original post, I considered them compatible. So you can explore the game world through "pretend" simulationist mechanics, or you can explore the game world through the story, a flexibility which 4E doesn't and "Legends" wouldn't offer.
The beauty of that flexibility is that it can support both playstyles simultaneously. That's a precious thing to have in a small rpg market. Isn't that what 3E had going for it, in its heyday?
Sure, there may be clashes and flaws. One player explores the world by throwing his PC off the cliff because the mechanics enable his PC to survive. The simulationist/immersionist player will be aghast -- he would never explore the world by throwing his PC off a cliff.
But if you divide that system further, to spin off a simulationist edition where a player won't throw his PC off the cliff because a) he thinks the PC would die, and b) the mechanics would equally have the PC die, then you've fractured the tiny RPG market such that you've traded a gameplay problem for a bigger marketing problem (not to mention the extra time and investment). Academic game design and a publishable ruleset doesn't exist in a vacuum.
I think it might be better, then, to have a 3E-ish "Lore" edition that is compatible with both playstyles, but unlike 3E, modular rules can tweak whether jumping off cliffs will kill you or not according to the group's preferences (same goes for wizards bashing down doors or not).
(OTOH, the 'do you want/are you ready for a D&D 5th edition' thread reveals a lot of indifference, so perhaps it is too late.)