This isn't a pages Google+ request. After a half hour of scouring Google's site I could not find either a dedicated forum to discus Hangouts, nor a direct reference to send suggestions to a specific department.
Google currently provides decent transcription of YouTube videos, Voice service, and probably many others I haven't used before. However, I do not think Hangouts uses live transcription. For those who are deaf or merely need help communicating, having this service would be beneficial.