Ahahaha. That's great.
I was coming here to post the same thing as a question... Because I feel like they're on a mission to replace all the core components for the look and feel.
Is this a stated mission? Have they replaced anything else "major" other than the window manager?
Of course, if it turns into something designed to takes away my freedoms, then I have to worry.
One of the great freedoms of open source software is to go "fuck you disty, I'm off to another one". When all your stuff is coded against Mir, Upstart and Unity, you no longer have that luxury.
Also, beauty is only skin deep.
For example, the *BSD's have a completely different init system and dependency chain resulting in a large "WTF" moment now that everything suddenly has crap loads of dbus in it as a core dependency.