Mark Shuttleworth: We Won’t Make the Same Mistake Again with Unity 8

So the important thing here is that Unity 8 won’t be forced on users as the default desktop, as a replacement for Unity 7, without users’ feedback. And that’s a very good thing right there! Therefore, if people want Unity 8 on their desktops, then only then Canonical will remove Unity 7 completely and replace it with Unity 8 on Mir.