Shuttleworth is rightfully proud of the work his team has done with Mir, but that is not the real issue. It seems to me that the community, or at least portions of the community, are upset because Canonical is doing something different, and they were not consulted beforehand.
What the many detractors of Ubuntu are missing though is that the system isn’t being built for them, it’s being built for everyone. The subset of the subset of the subset of people who use Linux, and the subset of them who use Ubuntu, and the subset of them who left Ubuntu and now use something else, and the subset of them who are upset enough about it to complain publicly are not the intended target audience. Canonical is not building Ubuntu to be an alternative Linux distro, Ubuntu is an alternative to, and competitive with, Microsoft Windows, Mac OS X, Chrome OS, iOS, and Android. Ubuntu is a system being built for people who have zero interest in their operating system, and are simply looking for the empowering freedom of a personal computing device.