The Mk8 currently has all of the pieces to do this... just a small software change to make it happen. Travel assist already adjust cruise speed to whatever the speed limit is.
I believe Mk8's built right now (MY22) will have the new speed limiter software.
For a little while the system will be active at engine start, but you can go in and turn it off - like lane assist.
Mandatory and non-user controlled will come later.
Difference in speedo readouts is not really a problem. Speedos are accurate these days, besides not running up the arse of the car in front is still the driver's responsibility - just like it is today. Its just a "limit" not a target!!