Canonical continues to delay the release of Unity 8/Mir, but the biggest reason for that delay lies in third parties, and the new world order for Unity might finally see the light of day.
The Unity desktop as we know it was officially released in 2011.
Read that again before continuing on.
Five years is a long, long, long — Windows XP long — time to retain the same look and feel for a desktop with few major modifications. This is compounded by the fact that Canonical has teased us with Unity 8 for quite some time. In fact, with the last few Ubuntu releases, the first speculation to be uttered out of every pundit's lips is whether or not Unity 8 will finally ship. We were all certain Ubuntu 16.04 would ship with the new Ubuntu world order. When that did not happen, the microscope focused directly on 16.10.
Guess what? It's not gonna happen. Not with 16.10. Instead, we'll get yet another release of Unity 7 that will make Ubuntu suffer one of the longest periods of boring release cycles in the history of computing.
Don't get me wrong, "boring" is not always bad. Ubuntu also happens to be one the most stable and polished distributions among the whole of Linux-dom. Of course, any desktop release that's had five years of polish (six if you count the alpha release) should be stable. If you install the latest Ubuntu release, you know you're getting a rock solid system...from kernel to desktop environment.
Even so, it's time. In fact, it's been time for something new since around Ubuntu 14.10.
Why the delay?
Most have gone under the assumption that the primary reason Unity 8/Mir has suffered delay after delay is due to instability issues and a lack of support from necessary software. However, if you take a gander at this most recent Ubuntu Unity 8 preview video (Video A), you can see that it not only runs well, but includes plenty of supporting software.
We've already seen that apps such as LibreOffice and The GIMP can run on the Ubuntu Touch environment and universal snap packages should make this all a no-brainer.
So why the delay?
I believe the issue is all about graphics support. Currently the only fully supported graphics drivers on Unity 8 are open source drivers. Even then, they only truly supported graphics drivers are for Intel graphics chipsets. In other words, certain graphics cards are, at this moment, out of luck.
Naturally, Canonical can't ship an Ubuntu release that is limited to only Intel chipsets. Even the Unity 8 Desktop Wiki makes it very clear that proprietary drivers do not yet have the necessary support for Unity 8/Mir.
That's a fairly sizable issue. Imagine if Ubuntu were to release Unity 8/Mir with such limited graphics support. Cats and dogs may not start living together, but there would be mass hysteria among the Ubuntu faithful. Now is not the time for such a setback. Instead, Canonical is better off holding Unity 8 until the support for proprietary drivers is available.
When will that happen?
That, my friends, is up to the manufacturers of those graphics chipsets. There is, however, good news. As of March, 2016 NVIDIA does now support both Wayland and Mir (see it listed here in the product description). The listing of supported products is fairly sizable, so that is certainly promising. That leaves AMD as the only major holdout. The only indication that I've been able to find, regarding AMD and Mir, was this Reddit thread that pointed toward AMDGPU supporting the Wayland graphics server. This should mean that Mir support will soon follow.
When should we see Unity 8 delivered?
I'm fairly confident that we will not see Unity 8/Mir in Ubuntu 16.10. There's no way the graphics support will be ready. However, I feel confident that Canonical will finally pull the trigger with Ubuntu 17.04. By then, proprietary graphics support will be rolled in and app developers will have had plenty of time to write their own XMir Wrapper so their apps will run on the Unity 8/Mir ecosystem.
I realize that every tech writer who covers the open source beat has speculated about the release of Unity 8/Mir and has been wrong every time. I do believe, however, Canonical is reaching a dangerous point of no return. The Ubuntu faithful have waited a very long time for this, and have endured quite a lot of boring releases. Canonical probably has one more such release in them before their user base starts to give up. I do, however, have faith that we will see a full-blown Unity 8/Mir release in Ubuntu 17.04.
And judging by the Unity 8 preview and what I've experienced with Ubuntu Touch, it will have been well worth the wait.