What I would like to see is more compartmentalizing and security/privacy improvements. As for the former it will help reduce overall complexity and should streaminline some development work, thereby making updates smaller and less buggy, which means more frequent polished updates. The latter just is something that needs to be done regardless. Users are entitled to their own privacy and data and how it should be managed.
Almost forgot, I would like for them to make windows update process more laid back. Not forcing updates and in the middle of working or whenever their algorithm feels like it.