The existence of two applications for changing system settings, the familiar 'Control Panel' and the touch-friendly 'Settings' app, was a point of major contention in Windows 8 and drew many negative reviews, criticising Microsoft's UI design for making things unnecessarily complicated. While Microsoft has made the Settings app much more capable with Windows 10, the two still remain part of the OS. That might soon change.
In response to a query by some Insiders on Twitter, Microsoft's head of the Insider Program, Gabe Aul, and a Senior Program Manager, Brandon LeBlanc, acknowledged the disparity and indicated that the company may soon retire the traditional Control Panel, in lieu of the modern 'Settings' app.
Gabe Aul further emphasised that two apps required duplication of code, more complexity and used more system resources. As such, one unified application would be "leaner". When this will happen remains to be seen but, as indicated by LeBlanc, some of the settings in the Control Panel have not yet been migrated to the Modern app. When that is complete, Microsoft will most probably remove the Control Panel from future Windows 10 builds.
Source: Gabe Aul and Brandon LeBlanc