oooh! That's a great idea! I hope someone out there who can do something reads your idea. Fortunately I have a bluetooth system in my car that dials, reads texts, and lets me answer them. I cannot, however, originate a text, and there are times when I would REALLY like to do that!
When I first set up my new phone I set up Cortana as my main Assistant, not knowing that I was then crippling my ability to use the Google Assistant. I have since learned that when you do that you can't get back the full functionality of the Google Assistant. I wish that there was a warning somewhere letting newbies know stuff like that.