My name is Olli Ries from Canonical and I am the Engineering Director for Unity and Mir. I wanted to give you an update on the roadmap for Ubuntu’s graphical stack over the next few releases.
Our Display Server Mir has gone from a proof of concept, sufficient to justify its announcement in March this year, to high quality, high performance component that we think will deliver the fastest, cleanest display experience for the Ubuntu platform. We are confident that all desktop environments and derivatives will work well throughout the transition, based on our ability to provide a full X compatibility layer.
Here is the roadmap and milestones for the Ubuntu graphics stack transition to Mir:
XMir on Mir by default, with a fallback session to X where there is no Mir driver support, supported for 9 months
Ubuntu 14.04 LTS:
XMir as default with the fallback session removed, full Mir driver support, traditional LTS support for 5 years
Ubuntu 14.10 and beyond:
Mir stack as default, including rootless X support for legacy X applications, supported for 9 months
XMir: X & Unity7 running on top of the system compositor Mir
Mir stack: Mir as system compositor with Unity 8 as session shell on top
Using Mir as a X compatible system compositor in 14.04 which can host any Desktop Environment that is running on X today, will allow all dependent Ubuntu derivatives to run on top of this stack in 13.10 and 14.04 without any changes needed on their side . Canonical is committed to support XMir for 5 years during the 14.04 lifecycle, which will give derivatives enough time to evaluate the graphics stack landscape and to make informed decisions when they are ready.
There is good progress in getting XMir into a distro ready state. A PPA  was setup to allow early dogfooding, daily landing tests will be turned on for the full stack (XMir, X, Compiz, Unity), automated performance test results are about to be published on the Ubuntu QA dashboard, inclusion to universe is on it’s way and we are preparing the MIR (see what I did there
for Mir ahead of Feature Freeze. Quality and ship criteria will be assessed and made available at that time.
However, please be aware that the PPA today is still tagged experimental/testing and will see rapid changes over the next couple of weeks. We will invite you for more widespread testing when ready.
Feel free to discuss any questions with the team directly here or on the mir-devel list.
Ubuntu will be the first Linux distribution to start replacing X as part of their default configuration. We appreciate your support and patience in that endeavor.
: various flavors running unmodified on top of XMir - https://www.youtube.com/watch?v=8h0m-ZjPxe8
: System Compositor Testing PPA - https://launchpad.net/~mir-team/+arc...ositor-testing