I am far less familiar with RE etc al than you are, but it seems almost like this whole immersionist/high plausibility 'feels real' is more agenda and things like purist-for-system seem more like ways to get it (technique/approach). RE never claimed to have exhaustively cataloged all kinds of 'S' so maybe there's an agenda that isn't mapped here? Or was his approach to just label these as individual genres and lump them within genre sim?
Well, RE puts it this way: purist-for-system prioritises
system over setting, character and situation. And colour and system are closely related in this sort of play (he mentions the "engineering textbook" flavour of GURPS; I'd mention Rolemaster crit tables and, to a lesser extent, spell list naming conventions).
On the other hand, what he calls "high concept sim" prioritises one or two of setting, character and situation, then mixes in the desired colour, and puts system last - because (as per my posts in the recent pages of this thread) system in this sort of play is flexible/malleable in the hands of the GM, whose job it is to narrate outcomes (like the bear) the will maintain the desired sense of setting, character or situation.
The ethos of Traveller, with its relatively detailed rules for generating animal encounter tables that tell us what life is like on the world in question, is purist-for-system. The ethos of AD&D from the mid-80s, with its instruction to the GM to
choose or set aside the random encounter result if another outcome would suit your game better, is high concept.
In my posts, I've been saying that purist-for-system produces a type of simulationist experience
for the whole table - because the GM as well as the players gets to see what comes from the application of the system during play. (Imagine, say, a Classic Traveller free trader game that is driven primarily just by the GM rolling on the various tables to produce worlds, cargoes, random encounters with reactions determined on the reaction table, etc.) There are two main risks in this sort of play, in my experience: (i) the mechanics break down as the fiction strays outside of system tolerances - this obliges the group to ad hoc things, or rejig their mechanics on the fly; (ii) play is (or becomes) boring, because the pleasure of seeing what sort of world the mechanics give rise to wears off (if it was ever there).
Whereas "high concept" produces one experience for the players - they get to experience the "cosmos in action" as narrated by the GM - but a different one for the GM, who has to make up the cosmos and so is not experiencing it in action. And this is where I have hit something of an impasse in this thread, as I am wondering what the principles/considerations/rubrics are that govern the GM's decisions about "what to say next" and am having some trouble identifying them. "Say a plausible thing" doesn't seem prescriptive enough to actually constrain decision-making, and is also part-and-parcel of all non-Toon RPGing. "Have no metagame agenda" seems to be belied by the idea that CR guidelines etc are something the GM should have regard to. So I'm a bit stumped.
