For a second, it appeared that a major clue was found in the images of the Start Screen which showed a date of November 28th in the calendar. Normally that would be seen as a potential launch date. But since that same date is used on the screenshots of the app for the Windows Phone 7.5 version, the November 28th date means nothing at all.
Getting back to the removal of WhatsApp from the Windows Phone Marketplace, the app's co-founder Brian Acton says a new version will be coming to the Marketplace soon. Considering that it has been free on Windows Phone and 99 cents for other platforms, when WhatsApp returns to Windows Phone Marketplace, it might come with an adjustment in price.
source: WhatsApp via WindowsPhoneDaily, WPCentral