(How) can I enable automatic switching between Intel and NVIDIA GPU?

Unfortunately as of today automatically switching between the intel and NVIDIA graphics is still not supported on Linux based operating systems. There is some progress to be seen in GNOME 3.22, where it is possible to launch an application with the dedicated graphics adapter, but only when the open source drivers are in use. Maybe this feature will be available for the proprietary drivers in the future. In the meantime, for Ubuntu I recommend to use the default solution nvidia-prime and to remove bumblebee, because this software is not maintained any longer ... the latest version 3.2.1 was released on April, 26th in 2013 -> Bumblebee Version 3.2.1 "Tumbleweed" - Release Notes !

Example of GNOME 3.22 - most probably the version which will ship with Ubuntu GNOME 17.04 :

We will see how this will influence the development of other Ubuntu editions and graphics drivers.