Oh God no. If we are going to stuff up our modern display server with hacky abstraction layer upon hacky abstraction layer, just so we can sub-optimally run the apps that now run acceptably everywhere because of X.org, then please, please, please, stop building replacement display servers. We're better off with X.org alone.
And the "What about having WaylandMir and MirWayland" is exactly the illustration of why Mir is such a stupid idea in the first place, it creates tension and technical problems where there need be none. If Canonical had poured the same amount of money and effort into Wayland, they would be running Ubuntu Touch upon Wayland already and they would be assured of being able to run all FOSS apps that currently run on X.org.
Now Canonical is taking a Microsoftian gamble that more developers will target Mir than Wayland and that they will come up on top because they have the larger application catalog and users will be enticed to solely use Ubuntu. I think that will prove to be a pipe dream, but hey, it's a ballsy move and it'll make a great story for the youngsters if they want to know what came before Wayland.