I don't think this means the 'end of email'. This seems to me like a natural progression. Before FB, Twitter and cheap SMS, email was the most effective means of digital communication. Now we have different tools for different types of digital communication. That doesn't mean email is becoming obsolete. It's a bit like saying mobile-touch computers will replace all other types of computers. I don't see that happening at all. Instead, we just use a number of different computers (in all shapes and sizes), for different situations.