I'm personally not too worried here. The thing is both Wayland and Mir will be able to run X on top of them, so currently all available GUI programs will still work.
What matters is the "winner". They will both hit mainstream usage, we will see which one is easier to develop for, and that one will take off. If Mir's claims of fixing input / specialization issues in Wayland comes to fruition, then it will probably win. If Mir hits like Unity, or atrophies like Upstart, then Wayland will probably win.
The problem is his Wayland fails everyone can switch to Mir. If Mir proves weaker, we are stuck with a more fragmented desktop space because Canonical doesn't change their minds on these things.
What matters is the "winner". They will both hit mainstream usage, we will see which one is easier to develop for, and that one will take off. If Mir's claims of fixing input / specialization issues in Wayland comes to fruition, then it will probably win. If Mir hits like Unity, or atrophies like Upstart, then Wayland will probably win.
The problem is his Wayland fails everyone can switch to Mir. If Mir proves weaker, we are stuck with a more fragmented desktop space because Canonical doesn't change their minds on these things.