Thanks Jason, yes this one! Having read through, I think I now understand...
Before the financial crisis, BMW was developing an ultra-luxury 4 door coupe (stock version of the CS Concept) + a "progressive" variant of the then future 6 Series with a hatch and suicide rear doors to be dubbed 6 Series Gran Turismo (announced by this red concept-car), to be marketed alongside the also progressive/unusual 5 Series Gran Turismo.
As the crisis hit, shrinking R&D funds put the stock CS Concept on slow track and turned the 6 Series progressive variant into something cheaper to develop (no specific rear end and interior, just stick 2 more conventional doors), more conservative, less ground-breaking and less risky. The idea of Gran Coupe was born, instead of the previously imagined 5 door/hatch 6 Series Gran Turismo.
So the 6 Gran Coupe has replaced the previously envisioned 6 Gran Turismo, and at the same time became a temporary replacement for the CS Concept although one range lower than initially foreseen. (However the latter has now resumed its development and will likely be marketed a few years from now as 8 Series Gran Coupe).
As such, it seems as though the 6 Gran Turismo was a wanted unborn child
so BMW decided to not show this red 2009 concept-car to the public. Instead, the new direction was shown in 2010 with the more classical 6 Gran Coupe concept (traditionally 4 door coupe closely based on the 2 door coupe). The 6 Gran Coupe would be the unwanted born child
Yet it seems to have gained general appraisal and to have generated potential siblings (6 Gran Tourer, 4 Gran Coupe, 4 Gran Tourer, 2 Gran Coupe). The 2 Gran Sports Tourer being the only real downscaled descendant of the unborn 6 Gran Turismo. So after all, the crisis shifted the tables in a good direction
Am I anything close to the truth?