Can some people confirm/debunk the statement that about 50% of the hashing power is concentrated in china? If that's the case, then I can see why that is a BIG problem.
It's a problem for decentralization...
I don't see having the majority of mining in China as a problem.
Even if China were to go dark, bitcoin transactions would continue uninterrupted. If a 51% attack is the concern, core should simply adopt our 51% attack defense system invented in 2013, a few years after Satoshi disappeared. It would need to be adapted and scaled, but it should work just fine.