It's absolutely inevitable that Bitcoin will be replaced.

Proof:
https://blockchain.info/address/1CounterpartyXXXXXXXXXXXXXXXUWLpVr

What is that counterparty address for?

You get whatever coin that is, for proofing you have destroyed some BTC at that address.

It's a good thing. This makes our BTC more valuable. Grin

I can't really understand the idea of proof of burn..

They basically lose their private key on purpose and the new coin detects this and gives them that coin. Instead of mining, you "buy".

So, it sounds like the new coin is "backed" by those bitcoin, but those bitcoin is not controlled by anyone and will very likely be lost forever...

No they ARE lost forever, irreversibly