Except for that $19 billion exit. Companies don't need to be turning a profit anymore -- they just need to prove they can scale, and someone else will figure out how to monetize it after a buyout. Hell, you don't even need to be a startup aiming for a buyout anymore to get away with being financially incompetent. Reddit is about to file their IPO at a valuation of $10 billion, even though they've been losing money for nearly two decades and are noticeably (and unsuccessfully) scrambling to find any presentable evidence that they're not complete buffoons.

Not true. They were charging $1/year from users in the richer markets. They could easily reach hundreds of millions per year in revenue if they followed this model.

~$30M revenue in 2014 from 600M users.

The vast majority of people will leave your service if it goes from $0 to even $1. So no, I don't think they could "easily" scale that up.

It didn't go from $0 to $1. It was always "$0 to most, $1 for those that really didn't care about paying because they knew that anything else would have much higher real costs"

Hell, If WhatsApp ever got to say "Facebook wants to buy us, but we are also considering changing to a pay-what-you-want model to avoid selling out", I'd easily give them $10/year without batting an eye.

Yes, but when I was younger, everyone that I knew, even digital illiterate people, paid that fee. Why? Because WhatsApp was (and is) everywhere.

A billion users IS a goldmine. Ask Google, facebook, twitter, reddit. None of these companies had any significant revenue for the first couple years.

They charged $1 per year before Facebook removed the fee.