3 years is a very short duration to reach 70,000 USD.
It is indeed a huge figure, however there will be an increasingly huge number of people waking up to Bitcoin too. The journey into the tens of thousands may well be an easier and quicker one compared to the journey from 1c to $100.
1 person getting excited in 2011 might be 500 people getting excited in 2018. Do the math as they say.
Of course it all go totally tits up too but right now momentum is still with it.