The big question you have to ask is what 1er will come.
BMW have big plans for its FWD family as with MINI they are projected to average combined 800,000 units by 2020 as BMW taps into demand for smaller cars.
Already we know about the CST , F.A.S.T. and the 3dr and 5dr City Compact.
But waiting in the wings if these cars prove popular with customers is a four dr and 5dr Touring , a cabrio is possible too.
With MINI investigating a four door option the combined two could offer the greater advantage.
With a Gran Coupe you have to take size into consideration , 6er Gran Coupe can accomodate the size as can the 4er Gran Coupe , but with the two the lower you get, taking into consideration proportions, headroom especially in the rear is why the BMW X4 and the BMW X6 will be the only Sport Activity Coupe models with the X2 taking more of a lower SAV outline. Simply because the concept cannot be completely downsized.
I seen the Mercedes CLA prototype in Munich the other day and having seen the car in Beijing the production car is actually taller than the concept for this very reason.
One design I have seen for the 1er/2er family is in the guise of a fastback-Coupe like model - A concept like this might prove the best option.