When you say that the reversal of a public key to a private key could certainly be possible at some point in time in the future, wouldn't that be the end of Bitcoin entirely? You are now talking about specific outputs, but wouldn't that possibility for reversal apply to any known public key? How would Bitcoin survive such an event anyway?
If we ever reached a point where quantum computers posed a realistic threat to the elliptic curve cryptography that bitcoin uses, then we would fork to a different quantum resistant algorithm to allow bitcoin to continue to move forward. Ideally this would be several years before any real threat from quantum computing, allowing everyone plenty of time to move their coins to these new safe address types. There would be a question to be answered at that point about what would happen to all the so called "lost" coins which weren't moved in time, and whether they were somehow locked to prevent them from being stolen or whether we just let them re-enter circulation.
I would also like to ask you where you got the number 2,828.654 BTC from? You have given some answers here to some research that I am into from time to time and perhaps you can elaborate or provide a source.
Certainly.
The theoretical current circulating supply is as follows:
(210,000 * 50) + (210,000 * 25) + (210,000 * 12.5) + ((784,963-629,999) * 6.25) = 19,343,525 BTC
Using the command
gettxoutsetinfo on a node will tell you exactly how much bitcoin is within the set of spendable UTXOs. Anything which is unspendable (such as coins which have been sent to OP_RETURN outputs, or coins which miners failed to claim in the first place) will be excluded from this number. This command on my node currently gives the following: 19,343,305.70780786 BTC
Subtract those two numbers and you get 219.29219214 BTC which is not in the UTXO set and therefore is not spendable.
However, there are also some bitcoin which
are in the UTXO set but are still provably unspendable. The main example of this is this transaction:
https://blockchair.com/bitcoin/address/s-272edf45031dd498e7b3ae89e11ff21b. 2,609.36304319 BTC have been sent to an invalid script which cannot be unlocked, and so these coins cannot be spent.
Add those two numbers together and you arrive at the 2,828 BTC figure I gave above.
For easier tracking, you can use this site (
https://bitcoin-supply.com/), which monitors all burned or otherwise provably unspendable bitcoin with a delay of just a few blocks.