Offer a quick and easy transition from autopilot mode to TACC mode. This would be handy in driving conditions for a quick transition. For example, the road conditions like sharp turns, bad surface or the poor markings on the road would increase the uncertainty of the autopilot successfully tracking the road and safely controlling the car.
Today, the only option for this action is to disconnect the autopilot, either with manual steering inputs on the steering wheel, to disconnect the autopilot with either pushing the autopilot stalk forward or to push the button at the end of the stalk, or to touch the brakes. After the disconnect of the autopilot, the TACC needs to be engaged.
This could be function with a pull on the autopilot stalk, when the autopilot is engaged, and allow this action to engage the TACC (and disconnect the autopilot). The ‘autopilot disconnect chime’ should sound when direct transition from autopilot to TACC is made, to provide feedback for the driver that they are controlling car with the steering wheel, not the autopilot.
I can't see any reason to NOT have standard cruise control. Most roads are unsuitable for Auto Pilot driving, but are perfectly fine to use standard cruise control.