I know, I know... D&D 5e is about being the "big tent" that brings all of the D&D players who were lost in the diaspora back home again. But is that maybe a pipe dream? Are the playstyle assumptions of the various "factions"--to say nothing of the mechanics preferences--simply too disparate to ever be able to be on the same page again?
Mearls' post mentions trying to design adventures with a pace and flow of leveling that matches a more "story first" paradigm of the game. He mentions the XP model as being more appropriate for a wandering hexcrawl or other "sandbox" style game. (For now, I'll reserve judgement on those two proclamations.) Essentially, he's saying that adventure writers are working in the "story first" paradigm, but hang on to the hex and dungeoncrawl paradigm of rewards. Why they would do this is unclear--unwilling to buck tradition, maybe? Hope that hexcrawlers or dungeoncrawlers will still see enough value in their Story First module to buy it anyway due to the rewards? None of these motivations are clear.
But if--and I say this for the sake of argument, because I'm not at all certain that I believe in this if--XP rewards are best suited for a hexcrawl or dungeoncrawl, and story milestone leveling up is best suited for a Story First paradigm, then wouldn't it be better for module designers to just pick a playtsyle that they're trying to accomodate and go all out to be the best module to accomodate that playstyle that they can? Trying to appeal to both playstyles seems like an exercise in pleasing no one very much. Why even go through the motions of appealing to XP progression, if it's inherent in the design of the module that the PCs are X level when they start it, and level up at Y position in the module, and are therefore at level Z for the remainder of the module? Just tell GMs that that is the assumption, and let them figure it out. If Mearls' column linked above is correct, that's what many DM's are already doing anyway.
I think the problem here is the commercial imperative that 5e gather in as many players as possible, combined with the psychological imperative some people have that wants everyone to be on the same page. That just simply is not a realistic goal. One side effect--whether intentional or not is up for debate--of the OGL was that gaming became micro-sourceable, in order to reach increasingly smaller niches. Actually, this was exactly what Ryan Dancey hoped it would do, but he thought it would do so under the rubric of d20 D&D, and I don't think he foresaw a Hasbro-compelled business desire to move to 4e, and then 5e in relatively quick order. Nor did he foresee the use of the OGL to create completely different games, like OSRIC and the rest of the OSR, and more particularly, Pathfinder. He certainly didn't foresee that Pathfinder would actually overtake D&D (as a brand name). Micro-sourcing to niche preferences is all well and good when we're talking about modules, but the actual game itself? Well, the OGL was supposed to drive sales of the PHB, right?
Then again, maybe he did. There were also a lot of comments from guys like Peter Adkinson and Ryan Dancey and the like about "saving" D&D from the poor decisions of corporate suits who didn't understand the hobby at all, and making sure that it stayed saved in the future, by creating an evergreen version of the game that could never be revoked. In that sense, Pathfinder is D&D; D&D as envisioned by the WotC team that saved it from the folly of TSR's mistakes, at least. In that sense, maybe it's more D&D than D&D is.
Now, I don't really have a dog in that particular fight. I don't really play Pathfinder, 4e, nor am I likely to play 5e. My group is quite happy continuing with 3.5, I think, and my own personal favorite is Microlite. I'm academically curious about stuff that happens in the OSR and in the "official" D&D space, but it's not likely to impact me or my own personal gaming very much no matter what happens.