If this is the case, why haven't we trained Echo devices to speak with Majel Barrett-Roddenberry's voice yet?

Between voice.ai and that audiobook John de Lancie and Majel Barrett recorded (Q-in-Law), I think it should be possible to run such a setup privately at least. Amazon would obviously need to get the copyright situation in order first.

Paired with projects like https://github.com/toverainc/willow I think you could recreate the Enterprise at home if you have enough IoT stuff in your home.