With the current demand trend price can easily surpass $2000 per bitcoin mark quite earlier than 2020 so i think price will be anywhere between 3k to 5k by 2020.
It depend on adoption how many new people would come into this, at the moment it looking so strong and recent growth is showing it will be over $5,000 by 2020, now bitcoin is getting more attention and we can see some bigger market giant are ready to take it as payment processor.
ADOPTION. this cannot stress enough. Theres only (max) 21 million coins people, less than half the countries some of us live in ;p
My guess by 2020? holy crap i would say 3k for sure. but it depends, all we need (besides consensus, but thats another topic haha), is some services like amazon or ebay to accept
BTC and its on imo. Dell does, thats pretty dece, newegg, alibiaba, to name a few larger places.
As they say, exciting times gentlemen