To get an idea of how likely it is, how many startups are reaching a $100+ million valuation in a given year?
See more here: http://www.paulgraham.com/invtrend.html
Actually, this article here has some good quantitative data. It puts the number around 200. It looks like most of the companies are non-tech/outside the Valley though.
http://bostinno.streetwise.co/2013/05/14/only-200-startups-p...