Vivo has refused to release source code for their smartphones.  Releasing the source code would allow third-party developers to make custom ROMs for users outside of China can fully utilize their smartphones.  Currently, Vivo devices use "Funtouch OS" which is made specifically for Chinese Users.  Funtouch OS lacks features for Global users.  Vivo has constantly used scripted responses when they are requested to release their source code, i.e. "I hope for your understanding for the stability of our systems" they will not release their source code.