+1 to explore using Wayland over Mir. I think it's intuitive that everyone (distros, developers, users) would benefit from unifying the Linux graphics stack to the greatest extent possible. The display server decision should not just be based on what is best for Unity, but what is best for the Ubuntu ecosystem as a whole. Having multiple display servers means there will be a duplication of effort for developers of application toolkits, window managers, and, of course, the display servers themselves. The proper question in my mind is whether all the additional downstream and lateral effort from maintaining multiple display servers is a bigger opportunity cost to the overall Ubuntu experience than the additional development necessary to get Unity running on Wayland. It's worth revisiting the display server question because this is something that may have major consequences for quite some time.