Developers working on Yunit and UBports (the two forks of Unity 8) have now decided to work together and one of their goals is to port Unity 8 to Wayland.
Based on preliminary discussions we had, we both agree that moving from mir to wayland is the direction we need to follow. Having that base common goal in mind, the reasonable conclusion is that we may not need to have two different separate repositories and that this will make developers' lives easier. On the other hand I believe that two different projects working with the same repo will create a real mess regarding management, decision making etc.
Those who had doubts about Mir's future, this might be the answer. Once transition to Wayland is complete, Mir will be essentially dead.