Speech to text is certainly getting better but it makes mistakes. If the transcribed text was sent over the link and then a text to speech spoke at the other end you'd lose one of the great things about codec2 - the voice that comes out is recognisable as it sounds a bit like the person.

A few of us have a contact on Sunday mornings here in Eastern Australia and it's amazing how the ear gets used to the sound and it quickly becomes quite listenable and easy to understand.