There is plenty of land available in places like Ramona. If the 67 was turned into a freeway, there would be a huge boom out there. The city is very opposed to development but things change. My house in Ramona had a view of miles and miles of undisturbed land.
People in LA live in Riverside and commute 2 hours each way. When land is scarce, they will just build further out. Although we are bordered by Mexico and the ocean, we can still expand eastward.