That is exactly the proposal that they want to do.
They want to bring back the Z3 (Which was originally the Z2)
Z3 will be with a Soft-top and Coupe. Z5 will allow the next Z4 to grow slightly larger as Roadster with a folding hard-top.
Z3 and Z5 will be the RWD offerings with the entry Z1 being moved to FWD and the UKL platform. Z1 will share with the next MINI Coupe/Roadster/Spyder.
Z3 and Z5 will utilise the modular platform within the F20/F30 models.