The Soft-Top is fake the new Z4 will actually get a folding hard-top roof like the 3er Cabrio and then the next generation 6er Cabrio. the reason being that BMW plan to launch a smaller roadster when the Z4 does a transitional shift similar to the 3er Coupe and move up a segment leaving the ground work for a smaller BMW Roadster which by all outcomes could be produced in it's key market the USA.

Z4 is more likely to remain as BMW do not want to overcrowd and make things difficult for the 6er product range. But the overall design will remain as headturning and modern with a futuristic slant similar to when the
Z4 was launched. To understand that the roof is indeed fake look at the additional side window as the Z4 and the Z3 did not have such a feature.

Huckfeldt has done a nice image previously but since then some details have been changed but the look is very similar.