So the answer to the question, even if you assume that yes this is profitable and it will rise upwards in the future, is this: We will implement measures that will make the attack so costly that it will be near impossible.
What kind of measures? Can you be more precise? Introduce them where? Bitcoin game theory relies on the presumption that the majority of the hashrate stays honest. There is no counter measure that can back the network up, if this theory fails.
You are talking about a very specific kind of attack, which is renting hashrate. This can be easily fought off with rudimentary measures such as increasing the coin maturity, making it extremely uneconomical to even try to do this as you would burn up resources before you are able to sell any Bitcoin to continue financing the attack.
There are always measures for other kinds of attacks or subattacks as well, the main reason we do not use them now is because they come with tradeoffs or changes:
1. You can implement some sort of finality mechanisms.
2. Any other kind of pending research ideas, I could look if you really wanted to but you should get the point by now.
3. You can completely dump the algorithm and render the attackers ineffective and in billions of losses in assets. Bitcoin mining machines are not useful for anything else.
In the worst case this is what we would do. You must understand that pure technology can not win this battle. We can take the blows, and the chain continues running and even balances stay in tact. It is going to be chaotic, turbulent, but
this is not something that can kill Bitcoin.
You must remember that there is no measure that solves problems for good, that is not how computer security works. It just makes them harder, more expensive, more difficult, or disables some particular cases. Do not expect a solution of a kind that is not possible for computers.
