Thomas Voß, one of the Mir developers at Canonical, wrote on his blog about some of the Mir work they are engaging in at Canonical and their vision.
Their requirements for their future graphics stack were tailoring towards EGL and OpenGL (or OpenGL ES), minimal assumptions about the driver model, ability to leverage Android GPU drivers, ability to leverage current hardware compositors, efficient use of memory/GPU/CPU, tight integration with the Unity shell, an efficient and secure input subsystem with mobile support, full testing all over, and adaptable to future requirements. With those requirements, Mir was started.
Perhaps most interesting and new from his blog post though is this bit: "For the closed-source desktop drivers: We are in active conversations with GPU vendors to enable Mir on those drivers/GPUs, too. [Updated] More to this, we are working together with NVIDIA towards a more unified driver model sitting on top of EGL."
We've known since the announcement that Canonical would be pushing for the binary NVIDIA and AMD graphics drivers to add the necessary requirements for running Mir. The interesting part though is the update by Voß that they are working with NVIDIA on "a more unified driver model sitting on top of EGL."
I haven't heard anything out of NVIDIA or other sources about this more unified driver model. EGL support though is nice regardless and NVIDIA will still need to continue supporting GLX for a long time to come due to their enterprise focus and that the X Server won't disappear anytime soon. EGL support will also benefit Wayland too and can be used on modern X.Org. Upstream X.Org developers consider GLX deprecated in favor of EGL.
NVIDIA's primary interest (and source for revenue) on the Linux side is through workstation customers, but after that, Ubuntu is very important to them and their desktop customer base so they are certainly listening and factoring in Canonical's plans. The same story goes for AMD and their Catalyst driver, but chances are NVIDIA will be first to the table with a nice EGL driver.