It looks like Whatsapp is expanding its availability for all platforms. It is already available for almost all mobile OS along with web version on desktop.
Recently, a twitter account WABetaInfo, which follows all the latest updates and details, posted some screenshots that give hints about Whatsapp desktop version.
The screenshots show upcoming WhatsApp builds and releases along with “Download for Mac OS X” and “Download for Windows” buttons that are apparently linked to desktop apps for both Windows and Mac.
Although, this is not officially confirmed by Whatsapp yet. but there could be possibility that the service is working on it.
WhatsApp native desktop apps for Windows and OSX would be nice addition and lets hope they become official soon.