I am glad that this thread was dug up out of the darkness because I find the topic still interesting, but for those "necroing" here please look at the date it was posted
The number of $5000 was the number often mentioned in 2018 when also the Bitcoin price was hovering around that, but today that number would be much higher (I guess > $20K or even $30K).
The mining floor is the basic cost of electricity, cooling and storage space for mining rigs. Versus the current price of bitcoin. If electricity, cooling and storage is greater than mined coins, mining operations are running in the red and might shut down. Basic costs IMO are not the biggest hurdle in crypto mining. The biggest hurdle is the initial start up cost of mining rigs. Miners must recoup the cost of mining rigs (hardware) before they can turn a net profit.
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The $5,000 floor number could be the average monthly electricity cost for a decent size mining op. But that would represent an industrial scale which should be mining enough net BTC for even a $5k number to not be a significant liability.
I think you understood the concept a little bit wrong, above all regarding your last two sentences; $5000 was referring to a price for 1 BTC, not to a cost the miner has to bear.
The "floor" I was talking about has to do with different price levels which could be described in several (slightly different) ways:
a) "the (minimum) Bitcoin price at which every miner which is currently mining will make a profit if he sells the coins regularly".
b) "the (minimum) Bitcoin price at which every miner which is currently mining will cover their costs if they sell the coins regularly".
c) "if the Bitcoin price fell below this price, then at least one miner will have to turn his equipment off"
d) "if the Bitcoin price fell below this price, then at least one miner will go bankrupt and leave mining forever"
These prices are slightly different in descending order from a) to d), it's possible the difference between price a) and d) is at least 20-30%, because miners can have some accumulated capital to continue operations before they shut equipment off or even go bankrupt.
The implications are also slightly different: a) to b) will probably not lead even to a drop in hashrate (but can "cap" the hashrate increase, like stompix wrote back in 2018); c) will lead to a temporary drop until the difficulty adjust, and d) maybe to a permanent drop.
But that doesn't matter that much. The point is that Bitcoin's difficulty mechanism is designed in a way that only an extremely fast price drop (let's say a sustainable 95% crash in a single day) could throw most of the miners out so a "death spiral" like it was mentioned above in the Coindesk article begins; even then "altruist" miners should sustain it. All these prices (a) to d)) are re-adjusted every 2 weeks when Bitcoin's difficulty changes again. They can also adjust due to other reasons, like the electricity price in major mining regions, price changes of mining equipment, etc..
Now again to the "price floor" - in the OP I described two variants which were mentioned in this forum; the first version makes reference to prices c) and d) (miners temporarily or pemanently shutting down, so less coins are "produced" for a while and supply goes down, which could have an effect on price), the second one to price a) (it could be more profitable to buy bitcoins than to mine them, so demand goes up). I dispute both, like I wrote in the OP.
So if the bitcoin price drops below the mining cost, majority of them would not shut off their mining operations. However, they might be more interested in buying bitcoins from the open market if this happens!
I dispute that, see OP.
Miners are already selling freshly mined bitcoin at a premium. There is a concept called "virgin bitcoin". Since cryptos are being used for many illegal activities, investors with deep pocket, usually wants to buy bitcoins directly from miners which are freshly mined rather than buying from the market.
The "virgin bitcoins" are indeed an interesting addition to the theory, although the premium the miners get isn't very high as far as I know. On a first glance, this could make it easier for miners to survive if price falls below their "profit threshold". However, if most or all miners sell virgin bitcoins for a premium, then this means that the hashrate is always slightly higher than it would be without that premium, so it levels out again - difficulty is then always a little bit higher, and it becomes more difficult to mine and get the premium. The price levels a) to d) would still stay intact.