They could still do targeted advertising and client side encryption. You just have some of the words hashed and sent to a third party web service that compares

They could still do targeted advertising and client side encryption. You just have some of the words hashed and sent to a third party web service that compares hashed words against ad words. With the right level of noise you could preserve both the security of the communications and offer targeted advertising. Or google could offer ad free encrypted gmail that costs money. There are plenty of business solutions to this problem and we will see many of them tried.