When someone give these kind of figures ($4400 in 2017), he also should give a proper reasoning or analysis to affirm it. I don't believe in this kind of soothsayers and prefer to be more conservative in this values. $2000 seems more credible, for instance.
If you look at past trends, you cannot push off any prediction like this to be unreasonable. He is talking about 10x increase in 2 years and is of course a possibility.