According to this article Tesla and BMW are allied to produce sport electric cars. BMW - Tesla alleanza elettrica per le sportive - Auto Sorry that the article is in Italian but you can easily translate it by using Google. According to BMW: “Entrambe le società si impegnano a promuovere lo sviluppo della mobilità elettrica a livello internazionale” (Translation) "Both the companies are willing to promote the development of electric vehicles at international level" Nice to see that BMW understood that the future of vehicles is electric.
I tried to find an English language article about that topic. I Goolged "tesla bmw sports car alliance" but could not find anything. It would certainly be a surprise if Tesla and BMW have entered into any kind of formal partnership to produce EZs. At this point I am skeptical.
Actually the above linked article mentions a meeting between Tesla and BMW to produce sport electric cars together. Maybe that there is not a formal agreement yet between Tesla and BMW.