With 450 M active users of one of the most pivotal services - messaging, WhatsApp is already an interesting catch for Facebook. But the best thing about WhatsApp subscribers is that in order to keep the service after the first year, they must pay a fee. Only 99 cents a year for now, but on a messaging platform, you can plug in an infinity of free or paid apps.
How many of these 450 M active users are actually paid subs? Probably much less than the half, since the bulk of the growth has been made over the past 12 months (e.g. 350 M active users back in October 2013). The key question is how many will want to pay knowing that Facebook will be tempted to peek into their messages and somehow monetize stuff. Beyond advertising, off limits according to Facebook; WhatsApp already pledges to bar ads, and Facebook needs new kinds of revenue streams, preferably CtoC or BtoC for a change. I bet that WhatsApp user fora are going to scrutinize any changes in the fine print of privacy and terms...
Business models are one thing, brands and platforms another: they too open up new horizons for Menlo Park at a time when churn rates get worrying.
Today, Google rules with the two most powerful search engines, its main service and YouTube... but both are free. Facebook already raised many eyebrows when it launched its vanity URL service precisely because terms and conditions opened the door to future fees, and a non-free Facebook could be the final straw for many users on the verge of deleting their accounts. Keeping WhatsApp as it is sounds a wiser bet to collect recurrent fees from hundreds of millions of endusers, but wisdom doesn't seem to exist in Zuckerberg's dictionary.
Anyway, the winner is WhatsApp founder Jan Koum: waiting one year before giving in to Facebook's siren calls proved very profitable for him.