So lets say that the Chinese government declares mining illegal & takes over the mines (likely to happen). Seeing that the vast majority of mining takes place in China, couldn't the government hypothetically reach over 51% of the bitcoin hashing power and basically centralize global bitcoin?
What cryptos, if any, are immune to this "51% attack" ? Is it even an issue? I'm not that well informed on the details of this subject so excuse my ignorance.
Essentially a change of algorithm or some sort of check of IP to block the miners in china (if possible).
I cannot see how to change the algorithm of Bitcoin. Is this doable? In regards to the blocking of IP address from the miners in China, this is a very weak defense for Bitcoin mining. They can easily use VPN and then they will appear to be mining in another country.
The best possible action for this is to have a hardfork then the remaining 49% separate from these Chinese and kill the other chain where the Chinese miners are.