I'm concerned about what that means for the future of Ubuntu, as it means lots of users leaving the distribution. Without a userbase, it won't matter what Canonical does with their display server.
I'd like to agree with you, that "diversification" does not necessarily mean "fracturing" and that developing one alternative does not negatively affect another. In most cases that's true, and it's one of the virtues of the greater linux community: whatever it is you want, it's probably out there.If someone wants to use an app on Unity that can't run on Mir then, yes, that user has a problem. It is, though, a problem with many, many parallels in the current environment. Not all apps, and certainly not all versions of apps, run on all systems.
The Ubuntu universe is already split and diversified in uncounted ways. It will stay that way, like the rest of Linux. Some people will build derivatives on Mir, some on Wayland, some on X.
Unfortunately, it's not quite the situation we have here. Canonical didn't simply develop an alternative to X11 or Wayland. Canonical promised to develop Wayland, contributed relatively little work over a long period of time, then dropped it in favor of their own solution while citing several bogus technical reasons for doing so (later redacted). This happened not long before the "Community" link vanished from the main site (back now, as part of the new navigation bar; explained, but not apologized for, in a blog post that reeked of "oops, we got caught"). Canonical has not been playing well with others lately. Mir isn't diversification, it's domination.
I don't see why they have to own the components to make use of them. I also don't see things like Ubuntu TV actually happening, but that's another topic. If Canonical had increased their contribution to Wayland, they could have had more influence on it and it might have been ready for distribution release earlier. Rather than contribute so something that could help everyone, they've decided to focus on what's best for them and them alone.Canonical, the business, wants to develop Ubuntu as a single platform that can run on all devices. That becomes much more difficult, and problematic, if Canonical lacks control of the core components that need to run on all those devices. That, presumably, is the reason they're doing Mir, not Wayland. Some Wayland developers don't agree with that, but it really isn't their call.
Not easy to define indeed. We have a lot of communities coming together to make what I think of as the Ubuntu community. To me this includes all the people who develop software that gets included in Ubuntu (which likely includes people who have never even used Ubuntu) as well as the users of Ubuntu and all of its derivatives (some of which are quite different from the source). That's a lot of people, a lot of a lot of people.I don't know how all this will impact the Ubuntu "community". Frankly, I don't know what that really is.
In the future, if Canonical sticks with Mir, many of those people will be cut off from the Ubuntu community, which will consist of only those people who develop for QMir (only the qt toolkit has yet been ported to Mir) and those who use the standard Ubuntu distribution.