This mule sports a softtop, rather than a retractable hardtop like the existing Z4. Whether this represents a final decision about what type of roof will be fitted to the production model is unclear. What we have heard, repeatedly, is that the chassis and the entire driveline will be pure BMW for both models, and that the main difference will be brand-specific sheetmetal. There are even rumors that an all-wheel-drive version will be available, or that the model will be available as a hybrid using Toyota's expertise in that arena.
It's been a long wait since the memorandum of understanding that lead to the mule you see above was signed in 2012, and we had expected an announcement that the roadster would go into production by the end of 2015, but that time has come and gone. Perhaps we'll find out more at one of the upcoming auto shows. Geneva is coming up in March, after all.