EpicureanDM
Explorer
This approach still puts control over rest - and therefore the difficulty of the game - in your players' hands. The decision becomes a little harder, but not much in my experience. You're still trying to connect a out-of-game balance mechanism ("How often should the characters recover their mechanical resources?") with an in-game fiction controlled by the people who are supposed to feel its pressure. To use a loose sports analogy, it's like a game where the rules say that the players can have three time-outs in a game, unless they decide that they want more. (That analogy isn't perfect, so please don't nitpick it.)This is why I believe our group needs to consider trying something like 1 average night = 1 short rest recovery value while something like a good night's sleep per week in a very cosy place offers the recovery benefits of a long rest.
If you use the system I described, the players' control over the game's difficulty is vastly reduced. You eliminate the awkward dance between DM and players as you negotiate whether the characters can rest successfully. You no longer need to worry about whether the players have "earned" a short rest or whether an unexpected long rest will destroy the challenge of the final battle. Each rest comes on a strict schedule that the players are aware of and can plan for. There's complete transparency. If they sling their spells too casually in the first three encounters, you'll see them carefully strategizing in the last couple of fights. They'll need to get creative (and you'll have to support that creativity) because they must make do with less. That long rest is still two encounters away and they can't weasel you into giving it to them early without a big sacrifice! So they'll figure out how to negotiate with the monsters or trick them or steal the treasure. And because you're mostly designing Medium strength encounters (mostly as defined in the DMG), you know that those final few battles will be reasonably short and quick, but still exciting.