One question is, how do they make money from that?
The operation is expensive. If they use it to mine, well, who cares? Let them, they work for us. If they use it to split and apply fraud, people will know, and Bitcoin value is likely to fall, they'll have the network and clients against them, etc... so many uncertainties. The danger of this attack depends not only on the value in BTC they can get (and that largely depends on value of BTC themselves) compared to the price for an attack, but also how much the BTC from reverted transactions are worth in the mess after the attack. I'm somewhat not afraid of a large company betting a lot of money on such an operation.
There's one more combination: the company doing it for mining, and a hacker or saboteur gaining control of the mining rigs to apply fraud for himself at the expense of the company's investment. That behaves like any large-scale hack on miners and might also happen if there's a security hole in mining software.
In the end, whenever I think of attacks of this kind, I come down the same path... what will the difficulty be, is high processing power good, is it necessary? I think low, no, no. But that's a large dispute in itself.
As long as we're minting, we have the great advantage that people happily provide their processing power. Remember that botnet? It just helped with mining and earned some money. Why would anyone risk loosing everything for a sub-100% attack profit margin when they can get a good bit of free money instead?
Are you quite sure? Traders on wall st. eagerly wait on the most obscure of financial news to profit from whatever price movement they expect. News from GPU manufacturers would be analogous to the fed declaring an interest rate hike.
That's no valid analog. Inflationary currencies are something completely different. The size of the newly minted bitcoins in comparison to the existent coins is shrinking every day, and with it the importance of mining within the market. Unless you can make assumptions on future trading fees -- *cough* again that subject *cough* -- you cannot tell whether miners will play a significant role in the future.
Of course, traders would expect price to rise if a large company plans something like that right now. Bitcoin is still small, surely price would rise if that were to happen. But if something else made the bitcoin market grow to a bigger size beforehand, relatively speaking, such an announcement would make only for a small change in price. The fed affects all dollars, miners just the corner they have access to. A very big difference.