The Metal RenderSystem backport from Ogre-next, that I talked about in the last round-up, now has landed in the master branch and will be available with Ogre 1.12.7. See the screenshot below for the SampleBrowser running on Metal
The current implementation pretends to have Fixed Function capabilities. Leveraging the unified FFP API introduced with the initial 1.12 release, this allows operating with a default shader. This shader only supports using a single 2D texture without lighting. E.g. vertex color is not supported. This is why the text is white instead of black in the screenshot above.
Proper lighting and texturing support, requires a Metal Shader Language support in the RTSS, which is not there yet. However, if you are mainly using custom shaders on OSX, you can start experimenting with Metal now. Furthermore, buffer updates are currently slowish, as staging buffers had to be disabled. Therefore, the Metal RenderSystem is tagged as EXPERIMENTAL.
Further development will happen at a lower pace though, as Metal neither has the large prevalence of D3D11 nor gives the synergy effects across platforms we have with OpenGL.
So if you want full Metal support in Ogre1, consider contributing and fixing bugs. The code was simplified during backporting, which shows by the size reduction from 14k loc in v2.1 to 9k loc that are now in Ogre1.