Even if China controlls 80% of the mining power that doesn't mean that we should fear a 51% attack. Do you actually think that the guys who control mining, being Chinese or not want a 51% attack??? of course not, otherwise their investment would be worth 0....
Come the halvening, their investment will be worth 0 (unless other miners stop mining/BTC price doubles), so not that improbable :-
Once the halving takes place we will see a lot of old miners getting of the boat. It wioll be uprofitable to mine for most of the oldest mining hardware. Since a lot of people will stop mining with their old hardware the most efficient miners will still be profitable!
Only if they're all paying the same price for electricity. Actual range is from 0 (stolen/dorm/mom's basement) to below $.02 (China, hearsay) to probably as high as $.07?
Yes, it is, but it is not only about electricity price. With so high difficulty maybe even more important is equipment performance. Everyone know that S5 now is in troubles.
On the market will stay the one who will win the technological race.
(In my opinion because of that Bitmain still not disclose S9)