The demand for every programming language / framework follows the bell curve. You are correct that Android demand will drop off at certain point. It's difficult

The demand for every programming language / framework follows the bell curve. You are correct that Android demand will drop off at certain point. It's difficult to predict what will be the next big hit. The best thing to do is keep an open mind and try out different things that has the potential to become very popular. It's like managing your stock portfolio. You have to spend time in some risky technologies which has big rewards, if it takes off.