Thats all well & good in theory, but things break down if the players aren't willing to risk the uncertainty. Take this example.
- End of the last long rest & players start things. No matter what there is always going to be a starting point & it doesn't matter if that was last night on the rail, back in town at the inn, or whatever. We shouldn't need to debate that at some point the players started with a clean slate because that's what a long rest does.
- Players go through a couple fights, lets say two fights.
- Alice the druid: I used a few of my big heals & only have one wildshape left, lets take a rest
- Bob the sorlock: Yea I could use a rest
- Chuck the fighter: Yea I used my action surge & took some damage even though Dawn the cleric healed most of it, I could use a rest
- Dawn the cleric: I don't really get anything from short rest but channel divinity & that's no big deal.
- Edward the wizard: um sure if we are taking a rest ok.
- Greg the GM: you don't feel safe taking a rest here. Remember this originak impasse...
- Edward: I'm going to cast tiny hut so we can make it a long rest
- Greg: You knew it was unsafe & a couple minutes into the ritual a wild encounter appears!
- Players stomp the encounter. You now have three fights.
- Edward: I'm going to cast tiny hut
- Greg the GM: a wild encounter appear... It's not very effective because it's only four fightsin
- Edward: I'm going to cast tiny hut
- Greg the GM thinks to himself "ok I can interrupt it mid rest" midway into the rest the party is attacked by a random/wandering encounter & still at four of 6-8 encounters.
- Lets say the party feels like they should deal with this instead of shrugging it off. Alice has recovered a wildshape, bob has recovered sorlock stuff, chuck has recovered action surge & second wind along with the possible archetype specific stuff like superiority dice. Dawn the knowledge cleric still doesn't really care but edward used arcane recovery. This has 2 ways f going... everyone pus out a ranged weapon & shoots from the tiny hut hunting blind or everyone but edward goes out to nova down the encounter & edward says the words "I stay in the hut to maintain the tiny hut & that's my turn".
- Either way the fight ends & everyone runs back to edward in the hut to finish the long rest & recover everything
- Greg the GM has the choice of trying again with a burrowing/incorporeal monster that can come up from under the dome or one that can dispel the dome, but both of those just go back to the earlier original impasse or a slightly modified version of it where people keep recovering short rest abilities until they either finish the long rest or Greg the GM is forced to throw up his hands in defeat. This is the second impasse.
You might say "well Greg the GM could setup traps or do x & y up ahead while the players are resting". Yes he could & people say that so often that I suspect at least one person will respond to this with examples of things for x&y. The problem there is
the original impasse. If X & Y are anything shy of abject & total TPK you just return to that point the moment there is a tiny dent in the party's combat resources/endurance. Even worse is that if Greg the GM does that the players are going to react by being even more cautious & taking even more rests. Greg the GM has basically no way to overcome the original impasse without resorting to fiat and simply declaring they can't because they can't or using a strict doom clock. Invoking oberoni or declaring that Greg should read the DMG because shy of rebuilding huge chunks of 5e itself it does not include things that will correct "no we are going to take a rest Greg. No. Means no.". Removing tiny hut doesn't solve it either because it just shifts things from the original impasse to the second impasse.
