Currently, the only way to use MyFaces with AS7 is to bundle it with the WAR and set WAR_BUNDLES_JSF_IMPL. This has disadvantages. One is that you must bundle MyFaces and its dependencies with each WAR.
The second disadvantage is that it will use the default MyFaces annotation and lifecycle handling. This is less efficient than using native AS7 processing via the SPI.
This feature creates a MyFacesAnnotationProvider and MyFacesLifecycleProvider that are only activated if Mojarra is replaced by MyFaces in the modules directory.
While use of MyFaces will require a bit of "hacking" in the modules directory, it gets us a step closer to fully pluggable JSF. And in the mean time, those who want to do an apples to apples comparison of MyFaces and Mojarra can test their application unchanged against each implementation. Thus, the community can start to gather legitimate data about which implementation runs better under certain conditions.