Don't warry about bitsoin. He is gona be fine
Talking about 51% attack no any mining farm can achieve that power and talking about decentralization of mining farm, it is normal to have most of the mining farm where electricity is cheap and mining hardware can easily be purchased. Sooner or later there will be mining farms all over the world when we will have many more mining hardware manufacturer.
Come on guys it's not a negative thread - it's just another question!
Anyway I think it's not an impossible thing to obtain a 51% of the power in one huge mining farm. As you're reaching such a more and more difficult computing level, every miner have to purchase newer hardware and so on. So if someone have the cheapest electricity cost and the cheapest new hardware it does make sense to even think about it. Nobody can start from 0 nowadays..