Evaluated meshes can now wrap other kinds of data (currently edit-mesh, in the future subsurf could be made to work too).
To ensure the mesh data is created, call BKE_mesh_wrapper_ensure_mdata, although this creates a full copy of the mesh and may add a noticeable slowdown in the case of heavy meshes and should be avoided by using the edit-mesh directly.
For more background see: https://developer.blender.org/D7169