The LXDE-based derivative of Ubuntu Linux has no plans to be using Mir, regardless of XMir or not.
While we know well that Kubuntu will be avoiding Mir
and is hoping to use Wayland once the upstream KDE software fully supports it, for now they want to stick to just an X.Org Server and not rely upon XMir.
The LXDE-based Lubuntu distribution has now also expressed their current distaste for Mir and want to continue using an X.Org Server. In particular, Lubuntu is worried about poor performance if using a compositing window manager. If you missed it, I have the first benchmarks of XMir
The Lubuntu Mir statements were made on the mailing list
and has been confirmed on the Lubuntu blog