some people enjoy other ways to play and that "fixing" a perceived problem, creates another problem for another group of people.
A quick example may be because the players actively sought out comfortable lodging and rest they regain all their HP overnight. Another example might be they players chose not to bring along camping equipment and bedrooms and they ground was wet and uncomfortable so they don't recover any HP that night.
I agree with TwoSix here, but I don't think that means I'm disagreeing with sheadunne.So you're arguing for a de facto resource cost for time. I don't think that's a problem, but it's still very social contract-y, and anything social contract-y should be highlighted in the game rules. ("The game works best when you play it this way.")
"Roleplaying out" the resting time - and so the GM can make resting a cost via adjudicating weather and terrain, imposing wandering monsters, etc - is a way of turning time into a resource, via GM force.
I do much the same in my 4e game - the PCs are currently in the underdark, and they can't just take extended rests willy-nilly. They need to find safe housing (with their duergar allies, say) or conjure up a Hallowed Temple (which drains their ritual resources).
Because in 4e it doesn't matter much how often the PCs get extended rests, there is no need for the rules to talk about how to handle the timing of rests. But this is different in Next, because of the assymetric suites of resources across classes. Given that, TwoSix is right that the rules should call out the need for GM force. And they should also point out that, because this is GM force not really mediated via the mechanics, the GM needs to be careful to be seen as fair and reasonable, not abusive, by the players. (Otherwise social contract can be undermined.)
The view that you impute to Mearls doesn't make any sense, though, without some further understanding of what the passage of ingame time means, and why it matters.I suspect that Mearls thinks the fast healing is (at least potentially) a good basic set rule because he believes the ability for PCs to get going again after losing hit points is a better default mode of play than requiring multiple days rest to restore hit points without magical healing.
If the rules treat that as self-evident, they will fail. When Gygax was writing his DMG he had the excuse that the whole enterprise was still fairly new. 30-something years later that excuse is gone, and we have excellent examples of RPG writing which can be simple and engaging and give the GM clear advice. (Moldvay Basic, Burning Wheel and Over the Edge are for me all standout examples here.)