Microsoft is building a brand new Cortana Notebook user-interface for the upcoming version of Windows 10, codenamed Redstone 4. Spotted on Reddit (via Thurrott,) the new UI is currently in testing with Insiders in the Fast ring, and can be found in the Cortana Notebook area within the Cortana search UI.
The new design is far cleaner than the previous UI, which to many felt unorganized and messy. The new UI is much tidier, with skills and personalization options categorized into specific areas. You can quickly configure skills, settings, reminders and more.
Windows Central understands that Microsoft is internally building an entire new Cortana UI for Windows 10 users. While not much is known about the Cortana redesign at this time, we understand it could change the location where users interact with Cortana. Perhaps this Notebook UI update is the first step in that change.