Windows 8.1 was released yesterday, with some changes to the search interface.
I've pushed out a new version of our Wikipedia app for Windows 8.1 which uses the new search box style, and fixes a few crashing bugs. The bug fixes (without the search UI change) are also available as an update on Windows 8.
Both Windows 8 and Windows 8.1 versions are available for installation via the Windows Store.
Note that source has been broken out from the older cross-platform mobile app to a standalone repository for future maintenance:
Repository view: < https://git.wikimedia.org/summary/apps%2fwin8%2fwikipedia.git/HEAD%3E Github mirror: https://github.com/wikimedia/apps-win8-wikipedia
-- brion