The best thing for avoiding any short-workday problem - and I speak here from experience - is to have players (and thus by extension characters) who have extremely low boredom thresholds. Then, whenever they start resting too much, all you-as-DM need to do is make it boring and they'll get their characters doing something instead of resting.
What, like play through the 1 hr lunch break or 8 hr nap in detail?
I'm sorry, that's not making the rest boring, that's making your game boring.
This is a bigger issue. The DM can not be the sole decider of both what encounters will be and when resource recovery can occur. The issue is that if anything goes wrong for the players then at that point it's solely the DM's fault.
Can the DM really avoid being ultimately responsible for both those things? I mean, even if he plays 'by the book' and 'hands off,' he's still /choosing to run that way/.
This isn't really true though. You are compensated with a lot of extra spell slots when you level. You get a large finite amount now instead of a quasi-infinite amount. The only limitation of the current method being how many rests will my character be limited to before he levels - which is mostly a character decision and thus infinite spells!
OK, this is an aspect I hadn't really considered.
Since 3.0, D&D has been a finite game. 20 levels and you're done. Really, it always has been, since it just stopped working pretty quickly as you got to double-digit levels, but it at least had these open-ended exp tables so you felt like it didn't have to end (you'd all be playing arch-magi and/or artifact-custodians or something eventually, but it didn't /have/ to end, in theory).
Even if the 5MWD were taken to the systematic extreme, you'd only have finite spells used in the course of adventuring, and, even if daily spells were systematically utilized in downtime, the lifespan of the character would render them finite (though HUGE) in number.
Compared to that, even several times usual n/day (and converting short-rest-recharge to n/day, which, given the guidelines, means roughly tripling them, IIRC) each level would be curtailing theoretical impact of systematic spellcasting.
But, I don't think you need several times. At apprentice Tier, the xp to level is equal to the daily xp budget, so extant daily slots should do it, at least to see you through to level 3. Level 4 it takes 1.5 times the daily xp budget to reach 5th, and from there, till you've hit 11th, it's over double. But not a lot, never as high as 2.5, for instance, tops is about 2 1/3.
Beyond 11 it wavers around 1.5, as low as 1.43 as high as 1.74(12-13, don't know what's special about that - 7th level spells? more likely just round-looking numbers on the table).
I actually think the extant daily resources would be fine to see you through a level, especially given that you might have plenty of opportunity to recover hps/HD during that level, so should need recourse to healing spells less often, and can also thus leverage at-will abilities more effectively. At first level, you'd be in about the same boat, but as you leveled it'd get more challenging.
OTOH, it might make sense to increase the exp required to level from 11 on up, or to reduce the daily resources at those levels, because, otherwise, the game's just going to get increasingly easy, by comparison.
SPOILER ALERT
Santa Klaus does not exist.
In DnD challenge is mostly setup by the DM.
Sounds like Santa Claus
does exist - in the person of the DM - the system can be as effed up as ever, the players as fractious as can be, and the DM will just set up everything exactly right to make his campaign perfect (or at least OK).
As the grognard cohort gets on in years, more and more DMs are gonna look the part, too.
