I'm late coming to this thread, so excuse me if I'm commenting on some discussions that happened pages back.
On Mike Mearls' articles discussing GNS theory:
Dungeons & Dragons Roleplaying Game Official Home Page - Article (The Many Faces of D&D)
He kinda did back in June.
On 4E being gamist, specifically the argument that 4E isn't a game that can be 'lost':
Somebody made the comment that 4E isn't exactly gamist as its difficult to die. The way I see it, death isn't the consequence of failure in 4E. I look at 4E more as a WWE Wrestling match rather than a boxing match. In a boxing match, two competitors face each other, one wins, one loses. In a WWE Wrestling match, the outcome has already been decided, but success or failure isn't based on competition but on entertaining the crowd. In 4E, the players and DM would function as both the wrestlers and the crowd, and the goal isn't so much to be challenging as it is to be entertaining and interesting. I don't see gamist as necessarily having to be either competitive or non-cooperative.
On new players and existing players:
There is one major point of conflict between new and existing players of a game, and that is the depth of the player rules. To appeal to new players, a game needs to allow them to quickly start playing the game on an even footing with existing players. Existing players, however, seem to demand an ever increasing amount of depth. More character options, more fiddly bits, more setting lore, more everything. 3E, 4E and Pathfinder put new players at a disadvantage, as a first time player isn't going to have the grasp of the depth of the rules. I don't even think Core-only 3E really accomplished this. 4E might have done a decent job at that at launch, but was quickly buried in crunch. Essentials was an attempt to create this, but wasn't as appealing as base 4E(with Fighters as deep as Wizards) and got a violently conflicted reception from the established 4E crowd. It feels more complete than 4E did at launch, but is missing a lot of what makes 4E what it is, like the aforementioned Fighter with just as many powers as the Wizard. Now, the modular concept introduced by Mearls might be able to accomplish this, but it will fail if no existing players use it in a newbie friendly fashion, and the big complex deep version becomes the default. I'm also not convinced that trying to make a single game cater to both is practical or wise.
On a simple core with optional add-on complexity:
The danger with this is that the core is tediously boring and uninspiring. Its going to be the first thing people reach for, and it needs to sell people on the game. If it is made too generic to facilitate the add-ons, people are going to tune it out. Something like this has worked in the past, as in White Wolf's base World of Darkness book and the individual games like Vampire, Mage, ect. but in that case the focus was on the add-ons, not the base system, and there was some history backing that up. I'm not sure D&D could pull that off.
On the schism in the D&D community:
I really think there are some irreconcilable differences, the biggest of which is the slaughtering of sacred cows. The 4E community has had some violently negative reactions to 4E bringing back some sacred cows(Magic Missile, Fighters who spam basic attacks). I don't really see any middle ground on this. I'm starting to think WotC might be better off with two D&Ds, one going forward and one keeping the traditions alive(a D&D Classic, if you will).
Is there math in need of fixing in 4E (among other things)? Yes. Is it overall a great game that lets my friends and I have a lot of fun when we get to sit at the table together every 2 weeks? Yer darn tootin'! 
