Dev Studio shall continue to be a vital tool in delivering Pega projects. It is not Pega's intent to rebuild all capabilities that exist in Dev Studio into App Studio.
The intent is to empower citizen developers to accomplish an increasing amount of Pega application configuration using App Studio, leaving Dev Studio as the studio of choice for "professional developers" (like CLSAs) to perform or finish off advanced configuration tasks.
Some of these Dev Studio tasks performed by professional developers include creating assets which can be utilized by those members of your delivery team who are less experienced with Pega configuration and working in App Studio, including:
Creating Data Classes with appropriate direct-inheritance paths, usable in App Studio as Data objects;
Creating User Interface templates for selection in App Studio when configuring a view for a process step;
Creating reusable functionality marked up as Relevant Records so that they can be discovered in App Studio.