Greetings, Min/Max Boarders!
Let me explain the title.
GNS Theory (Gamist, Simulationist, Narrativist) as it relates to D&D focuses on three aspects of the tabletop experience.
The gamist view is about participation and power.
The simulationist view is about creating, exploring, and interacting with a 'living' world.
The narrativist view focuses on what's best for the story.
I mention all these because D&D's first four editions (and their subeditions, like 3.5) cater strongly to these playstyles already. (These are based on my experience, and the accounts of trusted sources.)
1E and 2E are more rules light, emphasizing the narrativist view. The rules are largely suggestions to be heeded or ignored by the GM or group as a whole in favor of making a certain story happen.
Gamists and simulationists still have a place. D&D is, after all, a game with a focus on interactivity. Simulationists may get caught up in the grand fluff text and large variety of settings.
3.x and Pathfinder has a tremendous simulationist vibe. One of the goals of the d20 system was to be able to plug in real world values and have a real world-like result happen. 3.x and Pathfinder are also
far more rules-intense than 1E and 2E, meaning you're expected to know the rules
before you sit down to play so you can do it 'right.'
Consistency is a big thing: Having standardized XP progression across classes, saves, skill points per HD, HP, and so on makes things predictable for those who know what to expect. Second, we
finally got standardized rules for making items, even if they don't always apply! Thirdly, WotC and the occasional third party publisher have already created pretty much everything you're expected to need (and then some!) as a character, player, and GM.
Gamists and narravists still have their place. We're in a community that helps each other make characters (for power, as a pasttime, and for the lulz- I mean, the odd things possible within the game) and resolve power disputes. Plenty of people still make their own worlds and stories, but railroading is
very frowned upon.
Also, 3.x seems to emphasize making characters over making worlds. (WotC realized there was more money to be made catering many books to 4-6 PCs and players than one DM with advice that's largely universal across systems.) Faerun and Eberron were the most promoted 3.x settings with slight nods to Ravenloft, Oerth/Greyhawk, Krynn/Dragonlance, Planescape, and perhaps others.
4E took things to a very gamist extreme. My initial impression of the 4E PHB was that 4E is a game that admits it's a game. The world is mostly there as a backdrop to the action that is tactical minis combat. Abilities were divided into at-will, encounter, daily, and ritual, with rituals having 'utilitarian' or non-combat use. Other abilities were almost entirely for combat, be it the inflicting or recovering from damage or status effects.
4E also caused a
massive rift with its sudden shift to a gamist perspective. Simulationists were suddenly lacking rules that made sense. (What, no
flour in the PHB? NPCs exist only to facilitate the PCs?) Narrativists were split. On one hand, there was plenty of room for DMs to add their own stuff, though rule 0 has always existed in some form. On the other hand, if the world already requires so much disbelief to suspend, why will people go the extra mile to accept what I as GM offer?
And now 5E is on the way. From its preliminary announcements, it plans to have modular rules for 1E-4E styles of play. Even if it succeeds, I'm not sure where else D&D can go. It's satisfied the 3 main types of fans over the past 30-40 years, and each can claim his favorite edition, usually the one he grew up with.
D&D, however, is profitable. If it's profitable enough, people will keep making it, buying it, playing it, and changing it into something I don't yet know. The very definition of what makes D&D feel like D&D is personal and up for debate. D&D, to many, is synonymous with tabletop gaming or RPGs. It was a major innovator in its inception, but how else can it innovate enough to warrant an entirely new edition?