Spyphotos of what is supposedly the 991 GT3 RS circulated back in February but speculation was that Porsche included air intakes (which they have never done on a GT3 model, only the forced induction Turbo and GT2 models) for racing homologation purposes. There was also speculation that Porsche may not use the new direct injected motor due to these same racing homologation requirements.
Matthias Muller stated with in an interview with Auto Motor Und Sport that they know what is wrong and will make the changes to prevent this happening with the GT3 RS. Additionally, it appears there will be differences between the motors as he refers to the GT3 as having the 'other' flat-6 motor. How different these two motors are is unknown at this time.