That question is very complex and answer nobody knows. In 20 years maybe could happen something what we never thought. For example, 20-25 years ago Internet was not so important thing in our lives, but today, people cannot without it.
In modern time things are being changed very fast, even more that we can imagine. Only what we can predict for E-Commerce is to shipping delivery becomes faster, payments easier and safer, web shops to become much faster with thousands of products and so on. But these things are only to make performance better, here it's nothing new. As I said, nobody knows what will be the first crucial thing which will change E-Commerce strategy.