As the XT12GT was designed for throw (in a kind of compact size factor), the little brother should go in the same direction.
My guess for the XT12S is a flashlight with less overall length ans a noticeable smaller head diameter. To get the throw output, I can imagine the use of an optic instead of a reflector.
The 2-button UI on the tailcap should be kept. Maybe the internal charging option will be dropped to make the 12S smaller and less expensive.