There was Mir the protocol and Mir the library/codebase implementing the protocol. Since the Mir protocol and Wayland weren't that different — after all both we

There was Mir the protocol and Mir the library/codebase implementing the protocol. Since the Mir protocol and Wayland weren't that different — after all both were intended as replacements for X — it didn't take much effort to adapt the Mir library to use the Wayland protocol. (As for why Canonical thought that developing their own protocol was a good idea, I'm not sure, but based on what I remember reading about it from various sources — don't have links on hand, so take the following with a pinch of salt: 1. They, rightly or wrongly, thought that some bad decisions were made with Wayland 2. They preferred to have control over the protocol to be able to experiment / make quick adjustments based on their needs, and the experience they gained while using it in Unity8 (the main DE using the Mir library). 3. They were aware that porting the Mir library to use Wayland, if/once this was decided valuable, would not be difficult (as turned out to be the case). From a technical point of view, IMO it wasn't a completely terrible decision, but from a PR one it was.)