I personally do not expect any new M-mount lenses from them. Zeiss's lens range for their film-mount rangefinder is quite extensive, and I do not believe that they can be expected to cover all focal lengths in all extremes of aperture (they have never, in their past history, done that).
Zeiss has always (for 35mm photography, anyway) focused on making a conservative range of lenses with extremely stable and consistent performance. I think that they have done this. They have some world-beating lenses in M-mount (15/2.8, 25/2.8, etc) with performance that is not exceeded anywhere.
I don't think they will try to stretch the f/2.8 designs too much, and risk less-than-perfect performance.