He didn't tell the magazine which models would be cut, but noted that roadsters are continuing to struggle, and that was part of the reason BMW had pair up with Toyota to develop the upcoming Z5 and Supra twins.
Robertson also saw a trend towards 'four-door coupes', which have the benefit of easy rear seat access combined with the lower seating position of a traditional two-door coupe.
Dieter Zetsche, head of the Mercedes-Benz brand, has also publicly shared a similar forecast, telling Car and Driver and other media outlets, "The expansion into China and other emerging markets [has given] huge opportunities for sedans, but they did not take up these specialty cars".
With coupes and convertibles already a niche product, Zetsche warned that while Mercedes-Benz would always offer two-door vehicles, they may not come "in the variety we are having them right now".
Over the last decade or so, the German luxury car makers have substantially grown their ranges from just an entry-level, mid-size, and full-size versions of their sedans, coupes, convertibles and wagons.
Nowadays most also have a full set of complementary SUVs, as well as matching 'SUV coupes', and 'four-door coupes'. This is on top of an array of high performance variants and a smattering of specialty models.