BMW created a design for a BMW Z1 coupé back in 1998 but it never got the green light for production. The platform was used a few years after in developing a series vehicle. BMW launched the BMW Z3 roadster design in 1995 and after a few years, the BMW Z3 coupé was produced and sold in the market. The M version of the BMW E85 Z4 was in 2006 in both Roadster and Coupe variant. With the new generation E89 Z4, only a roadster model was offered.
Thus, a rendering from BimmerToday captures what they think the BMW E85 Z4 Coupe could have looked like. The design is based from the Z4 E86 and E89 platforms.
Source: BimmerToday