Just make the next Android OS Motorola exclusive for 6 months, and then Open Source it... They just have to balance between what they want to do and their OEM partners.
I think that's too drastic of a move, and would severely alienate partners, especially since Google has cultivated strong relationships with OEMs via their GED programs.
A more sensible differentiating move would be to simply strive for a better user experience and more seamless HW/SW integration in their MOT phones by leveraging their deeper understanding of the OS and the framework.