I agree that this adoption would make McDonald's an even more powerful corporation because of the growth of Bitcoin's market cap. But the most important in a cryptocurrency is not it's price, but it's the mass adpotion.
Bitcoin is a revolutionary international payment system and in a revolution there are always winners and loosers. I think Mc Donald's has already choosed his camp.
I hope we will see more big companies like that taking their ways to the future. Amazon perhaps (another rumour spreading these months) ...