There's another article by Mike Mearls on D&D Next, this time on XP. The main point is this:
From the perspective of game design, the difference between these approaches becomes important when we think about how best to implement rewards in published adventures. In the past, we've always defaulted to using experience point rewards for everything. However, for narrative-driven adventures like adventure paths, that approach can prove troublesome. Designers have to jam in the "correct" number of combat encounters to make sure the PCs level up at the right pace. Adventure design thus becomes a process of matching up the right flow of XP to the correct tempo of the plot. Otherwise, if characters don't level up at the expected rate, subsequent chapters in an adventure path become too difficult or too easy.
Rather than force the issue, a much better approach is to allow designers to present both options, and let DMs decide how best to run any adventure. This simple change to an experience point mechanic that's been in place since the earliest days of D&D helps to illustrate one of our critical guiding principles in the design of D&D Next. The game must provide options to support different styles of play—especially when it's clear that the default way of doing things no longer matches the way so many DMs run their games.
I really don't like this one. D&D has always been about experience and treasure as the main reward. You may or may not have some narrative thing going on as well but 4th Edition laid out a "Quest Experience" system to accommodate that. "Allowing designers to present both options" sounds fine but I suspect what that means is not sticking to our own rules for experience and encounter design - which is ridiculous.
Don't get me wrong in my current 4E campaign I have not always followed the number of encounters per level, and the resulting XP, by the book. There have been times I have told the players to level up for next time, regardless of the amount of XP they have actually gathered. The point is exactly that: I made that call.
The whole point of having a system is to show everyone how it is supposed to work. Individual DM's will vary their approach, but with a solid baseline out there everyone has a common reference point to use. Is D&D really going to have two experience systems, one showing XP/monster per encounter per level and one that says "wing it"? Why bother?
In the mechanics of the game there should be a solid system for XP's and progression. In the DM Advice chapter when discussing a narrative campaign there should be a section on the narrative level up approach. One is rules, one is advice. Everyone has a common reference point and (theoretically) everyone is happy.
Suppose some people decide to ignore initiative too and just start going in Dex order. Do we need to "support" that too? Within the rules. you cannot mechanically support not using certain sections of the rules! Leave that up to the DM's and playing groups.
There are lots of narrative style adventures and even campaigns out there. Typically they are for games that don't use levels and that's where they belong. In a level based game, a published adventure should stick to the system described for that game and leave it up to the DM's to improvise if they choose. Ignoring their own experience system would be a mistake in my opinion for standard D&D adventures.
This doesn't seem to be a difficult concept to execute - Pathfinder's been doing it for about 5 years now and is doing quite well by all reports. Maybe someone there could help WOTC out on this.
Plenty of other games do this just fine and I like a lot of those games. Having experience points and leveling up is one of the signature features of D&D and should stay that way. Sure, you can do it other ways, that's one of the fun things about the game. Let's not rush off and change it just because that seems cooler today.
There's a bit of self-fulfilling prophecy here too. If they would publish some sandbox adventures for this new edition, maybe the narrative style adventure wouldn't seem so dominant. I'll keep my fingers crossed.