Comment 1 for bug 1149581

My belief is that, in order for Unity to excel, it needs to detach from the "legacy of bad interfaces" that is represented by all the other desktop environments and display servers, and start fresh. If you look in the application store right now, you will find that 90% of the applications simply do not match Unity design guidelines or do not even have a friendly design, which is vital if Ubuntu really wants to succeed on this side.

Also, work on Wayland/Weston started in 2008. It is 2013, and, only now has it started to get some momentum. Ubuntu started work on Mir in June 2012 and it is already rolling it out to the public, with the first major release in October 2013.

If you read the https://wiki.ubuntu.com/MirSpec, you will find some of the reasons behind this "rupture", as well as the plans for compatibility with X11/Weston.

I like Ubuntu's boldness and I think it will only make other distros more aware of the need to be competitive.