WhatsApp could be working on a web client.

WhatsApp the most popular internet messaging service launched in 2009 has around 600 million users. The app uses Sim card for authentication rather than user names and passwords this restricts its use oy for mobile phones.
But this may change as guys on AndroidWorld.nl has while decoding the 2.11.471 version of apk  found certain mentions of WhatsApp web logging in and out of computers,tracking your status and latest activity in web sessions.

This type of service is currently offered by telegram and some other clients this could be biggest update to the WhatsApp and could prove to be more productive.

There is no mention of Facebook login in the code so The WhatsApp will web authentication could be done using QR codes or random codes or IDs. There is no official word on the matter but this seems very  likely to happen considering the pressure from competitors.