Imo, this has already been solved. I just whisper replies into my watch for both email and SMS. Google's voice recognition is finally good enough for this. I can't think of anything more convenient.
I'm not sure if AI-ish replies are something I'm interested in. Throwing complex fuzzy logic at what should be a hardware/interface problem seems shortsighted. I prefer a much higher level of granular control, especially if these messages are work related.