Let's say for instance "Mc Donald's" launch a new Alt coin, called "McCoin" and Billions of people starts to buy and sell these coins. What would the natural spinoff of this be? I think "increased awareness" of Crypto Currencies. A percentage of these people might start to trade other Alt coins or Bitcoin as a result of this.
In general it would have a good effect as it will make other people aware of what cryptocurrencies are but realistically I don't see any ICOs that will be more popular to BTC on its announcement date, you do have a good example as you have used McDonalds which I think as of right now is more popular than Bitcoin, them creating a cryptocurrency would boost awareness to the market but not all developers are as famous as McDonalds.