Disclaimer: I work full time on blockchain tech. My answers in order:
I've never heard the term private blockchain and therefore not sure what you are referring to. If you mean a blockchain that is exclusively mined and used by a single entity, I don't see the point. Perhaps people are piggy backing on the "blockchain" buzzword while creating something that is quite different?
A blockchain cannot exist without a currency/coin. Blockchains need a reward mechanism for miners who "protect" it and a cost for submitting transactions to prevent spam.
What keeps miners interested after all mining is done is an open question. As long as there is a reward for mining, there will be miners but if that reward drops too low, we could see the network's hash rate drop substantially (miners quitting their job) and the blockchain would become more vulnerable to double spending attacks (a single miner intentionally "undoing" a large number of blocks).
There is no fixed transaction cost, each miner is free to decide how much they "charge" to mine transactions. I wasn't aware that transaction costs had kept rising. Keep in mind that as the BTC/USD price fluctuates constantly, the average transaction cost in USD might change often while remaining the same in BTC.
In theory, the Satoshi client (original bitcoin) developers could release a new Bitcoin software which changes the Bitcoin consensus rules and anyone downloading this new release would be participating in a new "altcoin" which would be separate from the original Bitcoin. They could send or receive Bitcoins to people using the old software. For the Bitcoin protocol to change in a significant way, a large number of people would have to agree on the new rules.
Part of my questions were piqued by this blog post (https://blog.ethereum.org/2015/08/07/on-public-and-private-b...) which defined a private blockchain as a "blockchain where write permissions are kept centralized to one organization". I think that it might be the case of people piggy backing on the buzzword and that people are using blockchain as a sort of computerized ledger.
So, generally speaking, a coin with a larger number of loyal miners will be more resilient than another with less loyal miners?
I think I made a mistake with the rising transaction costs - in USD they have risen with the price of BTC but have been rebased a few times.
I've never heard the term private blockchain and therefore not sure what you are referring to. If you mean a blockchain that is exclusively mined and used by a single entity, I don't see the point. Perhaps people are piggy backing on the "blockchain" buzzword while creating something that is quite different?
A blockchain cannot exist without a currency/coin. Blockchains need a reward mechanism for miners who "protect" it and a cost for submitting transactions to prevent spam.
What keeps miners interested after all mining is done is an open question. As long as there is a reward for mining, there will be miners but if that reward drops too low, we could see the network's hash rate drop substantially (miners quitting their job) and the blockchain would become more vulnerable to double spending attacks (a single miner intentionally "undoing" a large number of blocks).
There is no fixed transaction cost, each miner is free to decide how much they "charge" to mine transactions. I wasn't aware that transaction costs had kept rising. Keep in mind that as the BTC/USD price fluctuates constantly, the average transaction cost in USD might change often while remaining the same in BTC.
In theory, the Satoshi client (original bitcoin) developers could release a new Bitcoin software which changes the Bitcoin consensus rules and anyone downloading this new release would be participating in a new "altcoin" which would be separate from the original Bitcoin. They could send or receive Bitcoins to people using the old software. For the Bitcoin protocol to change in a significant way, a large number of people would have to agree on the new rules.