From Fedora Project Wiki

Ideas for this include the by now classical cube rotation, or some kind of fade-out/fade-in. Fade-out/fade-in might also make sense for switching the audio from one session to the other.

Working kernel modesetting is a prerequisite for this.

Kristian has some handwavy stoy for how placing the X server on top of a small core display server will make this possible. See Desktop/Whiteboards/Wayland