Microsoft is planning to combine its Windows Phone Store and Windows Store into a single app store. Sources familiar with the company's plans have revealed to The Verge that Terry Myerson, head of the operating systems group, confirmed the move in an internal company meeting today attended by thousands of Microsoft employees. We're told that Myerson committed to the "next releases" of Windows and Windows Phone, which we understand to be Windows Phone 8.1 and a special update planned for Windows 8.1. Both are due to be ready in spring 2014.
Considering WP8 and Windows 8 share the same C++ code base, this does make sense and would be quite feasible.
For reference: Over 100,000 apps in the Windows 8 app store and 175,000 in the Windows Phone 8 app store.