Mir hasn't been doing a very good job at showing where Wayland is broken, but I think a key point that people are missing is that Mir might be able to work with proprietary Android blob drivers which would be critical to getting Mir to run on other smartphones other than the Ubuntu phone. Providing people the option to run Mir on their other devices, even if the manufacturer doesn't support it, sounds pretty interesting to me.
Does Wayland ever plan to get proprietary Android binary blob drivers working with their display servers? Especially considering that Android's linux kernel has a patchset that still hasn't been merged into mainline linux... I doubt it. Mir, it appears, has that as a critical goal that's going to be extremely important. Whether or not Canonical can pull it off is anybody's guess.
I'll bet you anything that Canonical is planning on running Google's Android patchset for the linux kernel and on top of that is going to be running Android device drivers in Mir to bring Ubuntu to all smartphones that can run Android today.