Ubuntu 16.04 Xenial Xerus still comes with the Unity 7 since Unity 8 is still under active development and may contain various bugs and missing features. But, if your wait is not getting over and you still want to install Unity 8 in Ubuntu 16.04, you can easily do so. In this tutorial, I will tell you how I installed Unity 8 in Ubuntu 16.04.
Note: Before you proceed, you must know that Unity 8 is still under development and you may face various issues and bugs.
And, it is not supported in Virtual Box. You can only install and use it if Ubuntu is installed in your system and not on Virtual Box.
To install Unity 8, open Terminal and type the following command (or copy paste).
sudo apt-get install unity8-desktop-session-mir
It will ask for your permission to download some files. Once done, this will install Mir and Unity 8 and you need to logout and login again to see the Unity 8 login option.
This is what my login screen looks like. You can see the option of Unity8-Mir, click on it, provide the credentials and you should be good to use it.
In case Unity 8 didn't work for you and you are not satisfied by it, you can uninstall / remove it easily to switch back to Unity 7 in your Ubuntu 16.04 system.
Type in the following command at terminal to remove Unity 8.
sudo apt-get remove unity8-desktop-session-mir
sudo apt-get autoremove
This will remove the Unity 8 Desktop and Mir and also the dependencies. Have you already installed Unity 8 and tried? How's you experience, tell us in the comments.