It's unfortunate because the GPU prices and availability right now are going nuts. I wanted to buy a GTX 1070 and it's out of stock with weeks of waiting on preorders on most European websites, with price increases of 40-50% in the last 30 days.
In the short term it may seem more unfortunate, but the problem with expensive ASICs is that they make centralisation far easier, by making it less feasible for ordinary people to do the mining.
The people behind sia coin believe differently [0] and after reading that I'm more inclined to believe them.
The short version is that since "commodity" hardware can mine many things, you can't gauge how much power there could possibly be. Someone with 100,000 GPUs could turn their whole system to your coin and have over 50% of the hashing power for a day, then go back to whatever else the day after.
With ASICs, the devices can't be used for anything other than that specific coin, so to "save up" your hashing power to sneak in a day that you can get majority hashing power would be stupid. You'd have to be giving up the income from them while you waited.
The article explains it much better than I can, I really recommend it.
What's stopping a government agency from "saving up" their hashing power so they could get majority control over Bitcoin if they needed to? Seriously, if you were the NSA, wouldn't this be a sensible thing to spend a few million dollars on? And they could use their mining hardware now, hidden through pools, so it would almost pay for itself. (Yes, I know I'm getting into tinfoil hat territory.)
In practical terms a 51% attack is not good, but actually has a fairly straight-forward solution to solve. Change the PoW. A 51% attack can't steal your coins, only restrict your spending them for the length of time they are conducting the attack. So the issue isn't that you have 51% attack possibility, but that people think you do, and furthermore think you're going to abuse it. If a government attacked it, they'd simply hard-fork away from the mining algorithm, and millions of dollars of hardware investment gets flushed down the toilet.
200K antminter S9 will produce about 50% hashrate of current bitcoin network that cost about 300M$ not counting electricity (200MW). But that means they have to R&D themselves these chips if they want attack quick. Otherwise they won't getting that much hashpower in one piece.
If they decide slowly enter game, attack price will raise significantly since network difficulty will be adjusted as they will add more of their miners into network and their projected 50% hashrate will be just 25%
So realistically its about 1 billion $ to attack current bitcoin network.
