In the current Windows 10 builds, when you do a search in the taskbar, you will have a small window for search results which overlays Start menu. According to Neowin, Microsoft is planning to change this experience in the upcoming builds. Instead of presenting search results in a separate overlay windows, Microsoft is planning to integrate search results into Start Menu itself.
According to our sources who have used the builds, searching will now be done inside the Start menu and do away with the overlay that currently exists in build 9926. This change makes the Start menu the functional area for searching and could be part of Cortana as well. Seeing as search is now inside the Start Window, it would makes sense that Cortana would migrate this way too.