By 2020 at list 40 to 50 percent of world population should own bitcoin and even use it. Many young men and girl has access to internet and bitcion is making great Wave all over the world and people becomes knowledgeable about bitcoin and others cryptocurrency.
Suppose for a moment that 3 billion people make 1 transaction, and suppose the average transaction is 300 bytes small.
The result is that blockchain grows 900GB, 6 times bigger than it is now.
At 1MB blocks this takes 18 years.
Before you think many people can use Bitcoin in 2020, calculate how few transactions blockchain can store.